I know someone who built a mobile "ham rig" that included a full featured P25, trunktracking scanner as the receiver. I don't remember what model he used.
He removed the scanner from the case, mounted it in a larger case, added a transmitter section from an old 2m crytsal controlled rig, added the mic and controls to the case, and added a trasmit/recive relay to the coax at the antenna jack.
His reason? That is now a homebrewed mobile amateur transciever that also happens to recieve public safety frequencies- and is thus exempt from laws that ban scanners in vehicles.