Select arbitrary triangles or vertices on the surface mesh as fixed constraints

Hi all,

I am doing a stationary analysis for structural mechanics.
I want to select some specific triangles or vertices on the surface mesh as the fixed constraints. However, it seems COMSOL automatically partition the surface into regions and only let users select the regions in the UI.
I wander if there is someway in livelink matlab to let me select arbitrary triangle or vertices as fixed constraints? This control ability is crucial for my current work. I'm very appreciated if anyone here can help...

Thank you,
Xiang