I'm having trouble understanding how someone can be exclusive with an agency.
Aren't agencies illegal in the first place? If so, they can't get damages or anything if you work as an indy. If the worry is that they'd drop you... Well... if they have genuine slow periods, are they really scouring ads to improve theirs, etc?
If it were me, I'd start writing up my ads, getting pics in order, etc, and plan to work under a different name with blurred face pics. While keeping the agency job.