Yeah, don't do it. IMO, at best McFadden and Bush get into a timeshare when McFadden returns. At worst (and probably more likely), McFadden will return slowly, get injured again and limp through the rest of the season.
You need WRs, not another potential RB mess.
Moverover, how many RBs who are mired in timeshares or stuck on the bench could you possibly want? Good lord, man. You already have Cadillac Williams (mired with Huggins/Blount), Forsett (will be behind Lynch soon), and Scott (only valuable if Benson goes down). Brandon Jackson looked halfway decent last week, but really he just broke off one long 70-ish yard run, and the rest of the day his numbers weren't great. Now with Finley out and possibly Rogers, Jackson will not have the benefit of a spread field.
If anything, IMO, you need to find someone who's desperate at RB and see if you can convince them to take C.Williams and Forsett, or find the Benson owner and trade them Scott (along with another mediocre RB) in exchange for an upgrade at WR.