I have the tall fuchsia ones and I think they would overwhelm most other plants. I know mine swamped my daylilies. They do look weedy but I love that fragrance.

I haven't replied because honestly I know very little about 4 o'clocks but I wanted to welcome you and I'll try to help.

Do they spread by runners? You might be able to slow them down a little by putting some edging around them and then plant annuals on the other side of the edging to keep them apart.
If you tell us how sunny it is and how tall you you'd like the companion plants to be, maybe we can make some suggestions. If it gets shade part of the day, tell whether it's in the morning or afternoon.

If you're getting lots of seedlings from your 4 o'clocks, you could try putting down several sheets of newspaper (in the area that you don't want them) with two or three inches of mulch over it. Then poke holes where you want to plant your annuals.

Are yours tall like mine? I have some that escaped to the edge of my yard; it gets no care and crowds out poke. I had some shorter ones broken colors that died out and the yellow leaved one did not ever take off. There are bulbs where my 4 o clocks are later so you can have spring bulbs in the area. Put a nice rock edge around it and add a gazing ball or bird house or something you like then be happy with them because you like them. Or put a bench in front of them.I like the big moths that zoom around them and the fragrance.