Hi,
I'm not sure that i correctly understand you and what exactly you expect, because if I'm not wrong the solusion is easy.
I'm using PowerShape v2015 but I belive that option is stil in future versions.
1) You have to create a 'Plane' from 'Creating surfaces' menu. (for details see attached file: 'Split_solid_by_surface_1.png')
2) Put your plane on a solid that you would split.
3) Make sure that all edges of your plane move over a solid surfaces
4) Click on 'Solid features' menu and choose 'Split solid' option. (for details see attached file: 'Split_solid_by_surface_2.png') - make sure that (splitting) solid is 'active' and, as I write above, all of the plane edges goes over the solid size.
