Dynamic system resolution for portal published BI content

Question

I have a Dev-Tst-Prd ABAP stack BI landscape with a corresponding Dev-Tst-Prd Java stack portal landscape.
My BI developers create reports and webdynpro applications which are then published to our portal and made available via iViews.  These iViews refer to the target applications via URLs which contain hardcoded hostnames and port numbers.  This makes it a pain when portal content is transported from Dev to Tst and then to Prd.
All my BI systems are known by the SAP_BW alias.  I have a different system definition in each portal for the SAP_BW alias pointing to the corresponding BI backend.
Can I use dynamic system resolution for this?  If so, how?
I want a URL like http://<devhost.domain>:<devport>/sap/bc/webdynpro/sap/appname to be transportable.  Obviously if that starts out as http://dev.mycompany.com:8100/sap/bc/webdynpro/sap/appname, it won't work when it arrives in tst where it needs to be http://tst.mycompany.com:8110/sap/bc/webdynpro/sap/appname.  If I could store the URL as something like http://<%JSP SAP_BW %>/sap/bc/webdynpro/sap/appname this could be transportable if there was something in dynamic system resolution to resolve the variable appropriately at runtime in each system.
As a Netweaver administrator, rather than a portal developer, I'm a little lost as to where to even start.

Answer 1

Success!  Thank you for your help.
What finally worked?
Create a Portal Component iView of type com.sap.portal.appintegrator.sap
Set URL Template to http://<System.wap.ITS.hostname>/sap/bc/webdynpro/sap/zcs_wd_cc_app
Set System to SAP_BW (where SAP_BW is an alias for the System entry for the system where we want the WebDynpro app to run)
Where did the help come from?
SDN (Mr Nicholls in particular)
SAP Help (http://help.sap.com/saphelp_nw70/helpdata/en/21/dfd241cb76c417e10000000a155106/frameset.htm in particular)
Where did the parameter value reference come from?
The "wap.ITS.hostname" attribute name came from the portal's system definition for SAP_BW.  Under System Administration -> System Configuration -> System Landscape -> Portal Content the entry for the SAP_BW system can be displayed.  In that system entry there is a field labelled SAP ITS host which contains the fully qualified hostname and port number for the ITS server delivering my application.  Expanding the detail of this field (click the arrow head beside the name) shows its Property ID to be wap.ITS.hostname.
So this last answers my earlier question about where to find the valid contexts and attributes per context for the variables to substitute in the URL template.  The contexts are the names of the fields available to configure the iView, the attributes are the Property IDs of the relevant information fields in the obect described by the context.
Note:  This solution ended up only being required for WebDynpro content.  The generated URL for WebDynpros appears to resolve any load-balance ITS URL to a specific host and port before publishing, the method here leaves the resolution until runtime - a great advantage in performance and flexibility.
The Web Application Designer published report content was generated in a transportable form already.