I don't know about the LoJack idea but there's a company called Snagg that makes the equivalent to pet microchips for musical instruments (My Carvin bass has one & I think Gibson Custom Shop stuff uses them too). These are small enough that they could be hidden inside a frame tube (manufacturers - maybe you could build them into bikes??) their retrofit kits sell for around $25.00 per chip - it may not aid in tracking but could deter theft in the first place by making stolen bikes easier to identify / harder to sell. Just my 2¢