Just for R3E, don't need to move the rest. So, you copy R3E to E:\ drive. Install R3E via Steam while pointing to the R3E folder on the E:\ drive (where it's installed).
I tried that, it wants to download the program, that it when it asks me to free up HD space. RRRE. APP
One way or another, I'll put it all in a separate folder in the raceroom folder in the steam e: drive now. Hopefully it does not need to download the whole 28gigs
When you say install you should get a choice of where to, and by moving the folder you have onto your "e" drive that should mitigate the dl size.