The only way I have found to do this is to play more than one household and by exploiting a quirk in the modify in CAS option. Tricky to explain, but I'll try.
You need two households containing sims set as played and testingcheats true.
If you meet a sim and want to add them to one of the apartments, then you can use the cheat you mentioned above. If I want to move that sim to another household, then there is no way in the game I can do that while in live mode, so I use the sim from the other played household.
I invite the other played sim to my played sims lot. Shift+click that sim and then go to CAS, Select the tick in CAS and when I return to the game I am playing the other sim's household, so now I can add my sim to that household and it is removed from my original household. You can then use the CAS quirk to switch back to the original household.
Make sense? If not, I'll try and clarify.
It sounds like a lot of fiddling, but has no more loading screens than the manage worlds option and means you are playing your sims from their perspective.
