R.G.
Hello, we had a similiar situation with our open staircase to the basement. We ended up with an Eddie Bauer wooden gate from Babies R Us/Toys R Us that we really like. To remedy the attaching to 2 post dilemma, my husband cut a piece of oak 1"x3" to fit the height and screwed it to the top and bottom of the post (we have a section that's square block on top and bottom). For the railing side he notched the oak piece and we ended up with a nice flat surface to mount the gate to. And in several years when the gate can come down we only have 2 holes on each side to patch instead of 10 or 12. I hope I'm explaning this clearly! If it sounds like something that would interest you, feel free to send me a message with your email address and I'd be happy to send pictures. Good luck! Oh, and our daughter can't open the gate, it's actually somewhat tricky but once we figured out how it works it was no problem to open one handed - very secure to keep the little ones out!