Does anyone know of a nonspecific (if that exists) caspase inhibitor or inhibitors of caspase-3 and/or caspase-8? in addition, what assay technique would you need to measure the activation/activity of a caspase?

Ok, I think that this is quite old so you might know by now. You can use an specific substrate with a warhead that binds covalently. 

There are several assays from luminescent/ fluorescent assays both in vivo and in vitro or commonly used fluotimetric peptides with tags that can be afterwards detected.