Will this be your first time on 4-aco-dmt? Honestly, I don't think you'll need anything to try to prevent a bad trip. The substance has a pretty positive push, in my experience. If you can stand being anxious for an hour beforehand, before you're dunked into the warm, cleansing waters of 4-aco-dmt, I'd say it might even be worth it.
Plus, I'm not sure another drug will "smooth" the come up, if you're idea of smoothing is to make it a gradual ramp up towards intoxication, though I may be wrong on this. Anyone else wanna chime in?
For me, 4-aco-dmt's come up was fast but pleasant. Shorter than a shroom come up, but longer than a DMT come up.