How can I trim the opposite side of a surface?

I’m dealing with a problem which should be utterly simple in my opinion. Basically, I’m trying to trim a surface using the Geometry.Trim node. It requires two Geometry inputs, plus a Pick Point. Now my situation is complicated by the fact that the only Pick point I can reliably extract from my model is the center point of my pattern element. This point unfortunately happens to ALWAYS be in the area of my pattern which I want to keep. But the algorithm of that Trim node is written so that the Pick Point area will always be discarded. Why there is no FLIP option is beyond me. See the screenshot below where I marked a few example center points in red. As you can see, that area will be trimmed away, and the outside part remains. I want the exact opposite result of that. Is this possible?

I was able to work around the issue by using the split node. Since I guess that this is sheer luck, I’m still interested in a proper solution, but for now, this is the setup I used for trimming instead: