I was under the impression there was an option to do this, but I can't seem to find it. I have a selection of UV Islands I don't want to move. I want to use the UV Layout tool to layout the rest of the UV islands around those locked islands. How should I do something like this?

I mean, I see a workaround where I could convert my UV Islands to point positions and create 3D islands, then boolean a grid to generate a new mesh representing the area between the islands and then use this mesh as a "pack into: islands from second input" option to layout on that mesh and finally convert those new point positions back to UV values... but it feels like maybe there's an easier way to do this that I'm not finding !?