I'm inclined to say using the KVM over RDC isn't possible, but why would you want to do it that way? Consider how it all connects together - the keyboard (& mouse & monitor) plug into the KVM, which in turn connects to the two desktop PCs, which are both on the LAN. The two PCs know nothing about being connected to a KVM switch - the double scroll lock press to switch is handled entirely by the KVM itself. Remote Desktop, on the other hand, is connecting to the actual PCs. Am I correct in understanding that you have a third PC on the other side of the house from the two on the KVM, and it is this third PC that you are wanting to work from. I.e. your setup looks something like this:
/-----\ control remote PC 1 /-----\
| | PC | |.........
\-----/ \-----/ :
| | :
=====================LAN====================== KVM switch
| :
/-----\ :
remote PC 2 | |......:
\-----/
If this is how you are set up, then when working from the control PC you can ignore the KVM entirely and just use Remote desktop on the two PCs. It is perfectly possible for you to sit at the control PC and have remote desktop sessions open on each of the other two machines, and switch between them at will.