Unfortunately I don't have a collet block, but mebbe I can make something. After noodling on it, I'm thinking of taking two pieces of aluminum, clamp them face-to-face with tape or paper between them, bore a hole normal to the top, rotate the aluminum to the correct angle, and mill the top so it will sit flat in the vise when it holds the standoffs.
I do have an indexing head, so maybe just make something to clamp the standoffs and bolt to the indexing head would be easier?
Thoughts?