I use a syringe (without the needle, of course) and squirt about 10 ml of warm water into the crop. The trick is to go slow, 1ml at at a time. Don't squirt it down the throat, because he'll aspirate. Under the tongue and let him swallow it. Once you get the hang of it, it should only take a few minutes. With a healthy, active bird, it's MUCH easier with two people.
Wait a minute, then massage the crop for 5-10 minutes. If you can feel the impaction, try to massage it in between your fingers. Not hard, but firm. The warm water will help soften, and work to break up the clump. I do it twice a day until it's gone.
I usually only withhold food for the first day. After that, I let him eat normally. That way, you can tell, in the morning, if he's digesting properly. The impaction won't keep him from digesting new food. That will only happen if there's a blockage. If he's only eating crumbles, and you're doing massages, the new food shouldn't build up on the current impaction.
That, almost, always works for me, within a week. If not, I would definitely revisit surgery. I know some people will use a docusate sodium stool softener. I've never done it, but you could look that up as well.