No, not really. Several entity types don't support an energy source. Belts and ammo turrets are the first ones I can think of. Without direct engine support, you're reduced to hacky scripts. I can't think of any way of scripting an equivalent for belts which wouldn't murder UPS and break and suck literally all the time. That's why there's no "powered belts" mod on the portal that doesn't have massive game-breaking drawbacks like literally deleting every item on the belt when it "loses power".
Some people get quite insistent about how it doesn't make sense that belts require power. Me, ammo turrets bother me more. I got over it.