Personally, I'd love to doing some CFI/CFII work just to get my foot back into general aviation...BUT...I don't think its worth sitting down across from my chief pilot and explaining why I deliberately broke the company's rules. There is no shortage of folks wanting a job at a major, and I think anyone who DELIBERATELY breaks those rules might get seriously hurt. (ie...terminated!)
Obviously, the stakes are dependant on how much you like your current job and your company's policy. I really don't know if this rule is a "wink wink, nudge nudge" kind of deal or hard and fast, so I just play by the rules and plan on keep trying to get a FDX paycheck or two every month.
One option for you under 30 types who need extra income might be a military option--flying in the Reserves or ANG. Lots of posts on those options and no company restrictions legally allowed on that type of work.
Other job options for pilots (away from flying) include perhaps ground instruction at flight schools, sales (cars, real estate, pharma...pharma....DRUGS!), professional work (law, real estate appraisals, etc), substitute teaching, construction or home repair, and owning a lawn care business. I know pilots who've done some of these, both to augument income and now to help ride out the furlough.
Maybe we could start another thread with "other jobs that dovetail nicely into an airline lifestyle".