No you can't. Not in the 360 version either. Just another example of the stupidity and laziness of EA.
Apparently, they didn't want cheezers online putting WR's at TE or CB's at DE for example.
What they didn't realise is that it would totally screw up franchise mode for people. When my starting left guard got placed on injured reserve, I couldn't just move one of my 5 offensive tackles over to guard. No, I had to sign a free agent guard. And in order to do so, i had to cut another player from my team, because EA forgot to make it so that a player placed on injured reserve, would free up a roster spot, like it is in the real NFL.
"If it's in the game..." my a$$