Initiate Application Installation from App Catalog via Command Line / PowerShell

Question

Hey Guys - 
We have a single, fairly extensive OSD task sequence which covers systems for all departments.  Due to it being a single TS for all, PC Lab techs must manually install some apps after it finishes via the Application Catalog.  In past environments,
I've used MDT's UDI Wizard to create a frontend where techs could select additional software they wanted installed during the TS and it worked great!  I'm trying to get something like that approved now, but in the meantime told the techs I'd come up with
a temporary solution to make their job easier.
Enter WPI (Windows Post Installer.)  Back in the days before I used SCCM OSD and relied in Acronis images (yuck), I used a the WPI tool which only ran once - at the first login - even before the desktop
loaded.  It's highly customizable and basically shows a single window which lists any applications or scripts (in groups) which you have configured.  You place a checkmark beside each one you want to install, click the "Install" button,
then watch it's installer frontend install each of the selected apps.  Once done, it either restarts the PC or exists to the desktop.  For each application I can add, I'm provided with a few options to
install it.  Obviously, an installation command line string field, but also a few more like installation order, requirements, and dependencies. 
My Question
Each of the applications I've listed are in our Application Catalog and are advertised to All Users.  Even though I could simply point the installer string to the app's source path and use the same string that the SCCM Application uses, I've been asked
to do something different.  Instead, I'm trying to find a command line string which when run would perform the same action as if a user had selected to install an Application from the Application Catalog.
My thoughts are that if this is possible, it would probably be in the form of a PowerShell string - not just a basic command line one.  Since WPI has a frontend which shows the progress of each app's installation progress as well as overall progress,
it's designed for the installation strings to install the app silently.  Therefore, I would much prefer my solution run silently as well if possible.
So... does anyone have any idea for how I can make this happen? Thanks!
In case it makes a difference or answers any questions, below are two screenshots showing most of the fields and options which may be used to configure how an application installs in WPI.  I couldn't include the Dependencies one since I could only
attach two images to my post.  Also, the manual for WPI is embedded in the application's
download (ZIP) and not a page on their site.  For the examples below, I used Google Chrome, but didn't configure anything besides the application's name:
Application Detail Options
Application Command Options
Ben K.

Answer 1

From what I'm reading, you are working towards MDT but it's not approved yet, so the goal is to:
Deploy a "bundle" of applications as painlessly as possible without using UDI to make customizations quick.
Lets talk options then.
Option 1:  If machines types are in a unique OU or security group, create a collection for that and set these applications to mandatory install.  After initial deployment, the provisioner can drop the computer in the proper OU or group and you're
good to go.  Downside:  collections refresh plus client check-in makes this less than instant.
Option 2:  Orchestrator.  You can write a runbook that will approve and push apps.  You can then use the Orch console front end or a more friendly sharepoint/SM portal to push things out like a Manager would approve apps.  Downside:  if
not already deployed, there's no way they would approve that infrastructure if they are hesitant about MDT/UDI :)
Option 3:  PowerShell and WMI.  This should be doable ... but I've never tried it.  It looks like you're headed down the right path ... but i guess my question is:  if you can't have UDI when do get to pick the app?  Are you planning
to write a full multi-box for them to check their apps after the fact?  In that case ... just have the appcontroller URL pop up on first login ... might be easier than reinventing the wheel.