Applying effects to selective frames in a video clip

Question

Question: What is the best way to add a mask only to certain frames in clips of a sequence on Premier Pro CC using After Effects (i.e., a single frame mode)?
I am trying to fix a keyed video, but only need to fix frames here and there and  do not want to animate it.
In the past, I have used the following methodology:
SUMMARY: Remove, modify, render, export, and then re-insert each frame that needs to be fixed (one by one) starting in Premiere Pro (CS5, CS6, or CC) and using After Effects (CS5, CS6, or CC) using the following steps:
1) Open a timeline with the entire video sequence
2) Cut the frame that needs to be fixed out of the timeline sequence, basically leaving a one frame hole
3) Apply the mask, filter, or other effect to the frame within After Effects
4) Export the modified frame in the format of the original sequence (recommended) as a new one frame clip
5) Import the result back into your open Premiere project
6) Drop the imported one frame clip back into the original sequence in the spot where it was cut from
7) Repeat for each frame
8) Finally, re-export the entire project to the final desired format.
There has to be an easier way than this.
NOTE: The cross-launch function between Premiere Pro (PPro) and After Effects (AE), where a new AE project is opened by selecting this option in a PPro project/sequence, is very confusing and awkward to use, and has never been useful for me when doing other operations such as Color Channel modifications or channel replacement/swapping. So unless there is something within this function that will do the job, and then re-create the new video export faster, then I have ruled using this out.

Answer 1

If you just have a few frames to mask then start your mask in a safe spot just start your mask where you need it to work, animate the mask for the few frames you need, then,  when the mask is no longer needed move forward one frame and move the mask clear off the shot. Copy the mask keyframe, move to the first keyframe for that mask and then back one more frame and paste. Your mask will now be off the shot completely, jump into position when needed, then jump back off the shot. Problem solved without splitting layers or doing anything else funky with the shot.
In many cases, if you need a lot of masking to fix a key you can solve the problem with another instance of your keyed (Keylight) on a duplicate layer and then use that copy as a track matte for the first. I do this all the time. Sometimes I'll have as many as 4 or 5 copies of the footage, all keyed differently removing different parts of the background, each with a different garbage matte, and then combining them all using track matte to produce the final plate for compositing.