Hey I am planning to do that with my new RG 320 FM so there were two good sustainers to go with. One option is to buy a good old fashion Fernandes sustainer is really nice besides getting it installed. the other option is to buy an EMG active pickup and in this way routing is not needed because the sustainer is under the pickup. Plus if you ask me, EMG's are some of the best pickups around and there are a number of them to choose from. Any how i plan to get an EMG active 81 cause they are the best for the lead guitar's sharp and cut-through sound. Well best of luck tryin to decide what to get as a sustainer.
laters.