you cant atm...
yac uses scrypt-jane, and is/was designed to be cpu mined only..
If you could, it would be the end of yac, as its core ethos would be pointless
If you think a GPU miner can't be coded for it, you're mistaken. Both chacha20 and keccak have faster throughputs than salsa20 and sha2-256, and the value of N right now should provide extremely good GPU performance.
Basically the first person to get a large GPU mining farm on this will shred the network -- assuming this hasn't already been done.