As for the mid air intercept and subsequent formation there are plenty of products out there that work with an Ipad and allow reception of other aircraft ADS-B data, so no need to turn the aircraft transponder on. Just two examples are shown below, one of which also has an AHRS ability!!!
There is also a lot of navigation apps available for Ipad that would allow someone to accurately fly a predetermined route just using the aircrafts HDG control.
XGPS170 - GPS + ADS-B Weather and Traffic Receiver for iPad and Android Tablets | Dual Electronics
iLevil - ADS-B AHRS GPS