I've established a relationship with the local traffic engineer. I'll email him and report unresponsive ground induction loops, and he'll promptly send out a crew to adjust the sensitivity and/or mark the point on the pavement (yellow reflective stripe, about a foot long). I always try to thank him after the adjustment has been made, and it's worked out pretty good.
(The traffic professionals, unlike many SOV motorists, recognize the value of making the infrastructure as bike-friendly as possible. After all, a bike on the road usually means one less car on the road.)