We feed ASFs live. Make sure the ASFs are well fed and watered. I feed on a separate feeding tank because I have this heavily decorated tanks for my bps with lots of nooks and crannies that an ASF can hide in and I don't want rat poop in there either.
So, I put ASF with a lab block (yeah, I feed Mazuri 6F) in there, add the snake, and wait a while with tongs in hand for just in case. They're like "deer caught in headlights" when the snake is put in - they freeze and do not move for a long time...