This is what I did for a guy with a similar situation:
Note: This worked on a television that had discrete inputs to Video inputs and tuner.
On the home page I created a PIP button that jumped to another home panel labeled PIP. This panel asked the question "What would you like to have on the small picture?"...Icons displayed the names of video sources...DVD, VCR, TV, DSS, whatever...and a PIP off button. Those icons macro put the tv to their designated input. It also turned on PIP (toggle), and then swapped. Then the remote jumped to a device panel labeled PIP. (You'll see why in a sec). This panel asked the question "what would you like on the large picture?". This panel would have the same icons as the home panel, minus the one the selected for the small picture. When the user selected the large picture, the macro selcted the right video input AND told the receiver what input. Then it jumped to the large pictures transport panel.
Now the easy part. When you hit the home icon, the remote goes to the last home panel you used...the PIP home panel! If the user wants to swap or change sources...boom there you go. Or the can turn PIP off, which that button jumps to the main home panel as before.
