You can, but you'd have to find which specific R5 graphics cards it supports and use any one of those cards. I wouldn't recommend that though, seeing as it's an R5 series, and AMD is currently on R9 and soon to release their new R9 300 series. I'd go with the best AMD GPU you can get right now or wait for the Fiji architecture. Don't worry about Dual Graphics or even Crossfire. 1 GPu will do fine.
To Lag: Installing a dedicated graphics card does not shut off the graphics function of the APU. It merely substitutes the dedicated GPU for the APU as a graphics source. You would have to go into the BIOS and turn off the APU graphics manually. I wouldn't recommend this though, since that cause graphics for me to go totally off even when using a dedicated GPU.