The clamps are only mild steel.
The bolts may or may not be stainless.
We use stainless in our racks but I have seen chrome plated steel bolts also.
Hit them with a good anti-seize spray and let them sit overnight first.
Use a vise, with appropriate protection of course, to hold the clamp.
For screws this small you really will want to use a decent drill press for the drilling process or things can get ugly fast.
If you find they are stainless drill slowly. Stainless isn't really hard it is more abrasive and brittle but use High speed and it will work harden the stainless and then your screwed.
Your going to want to get the surface of the screw flat first so you can center drill the bolt before even starting to try and drill it.
On small screws like this it is imperative that the hole be centered or it can make it dramatically more difficult when trying to use an EZOut.
A Dremel with a cut off blade will do the trick.
Use a cobalt center drill then use a left handed cobalt bit, as PK recommended, then an easy out.
Heat the clamp first, to help the process, before drilling and before using the EZOut if the bit does not get it out first.