Hey Daniel,
We'd planned on adding GAC support to wyUpdate but there hadn't been any user demand for it (until now, that is). We'll add this to the next bugfix release (2.6.19).
Quick questions: I've talked to people about this, but the response has been mixed. Do you keep the file *and* install to the GAC, or do you just install to the GAC and don't leave a file hanging around?