I get what you're going for and if BG3 had a live DM you could probably do this on a situational, RP basis. You could even have some scripted situations but it would be very difficult, if possible, to program what you want into an open world CRPG. I have used, and as a GM allowed the use of, the Sleep spell outside of combat to get past guards and such and I could see that being a good addition to the game but inside combat it's a different issue. The Sleep spell is not difficult to wake from, all you need to do is "attack" the target and they wake immediately, this would include a shove or an attempt to immobilize them, so what you're describing just isn't possible with the spell as it is written. You'd need to change how the Sleep spell is written in D&D to work to get the result you want.
