How to mount leveling spikes in a granite plinth?

The issue is getting the nuts that hold the spikes secured in the granite. Drilling holes - is this something a supplier will do? Best adhesive? Potential pitfalls?

Any recommendations on granite thickness or good VFM spikes (I have thick carpet) appreciated as well.

I'm still in the thinking stage on this and wanted to gather some basic info before I start calling local suppliers. The plinths would go under my floorstanding speakers and Isoblue rack.