Hi Creamyjalapeno (great name BTW),
I don't think it's possible to remap the keyboard equivalents for the on-screen remote. Have you tried parking your mouse over the Last button on the on-screen remote ? Perhaps there's a command other than enter that will do it. If there's a different keyboard equivalent, it should pop up as a tooltip. On my Mac, it's Ctrl-L. On Windows, it might be Alt-L.
If you can build (or have someone build for you) a custom remote that has the Last Channel function moved to a different on-screen remote button that has a keyboard equivalent, that might work too.