[aerohead]

All I can think of is the old school 'shrouding trailer.'
The test vehicle is enclosed inside this trailer, which is essentially airtight.
It is 'pulled', in neutral, or with the driveshaft disconnected, by a tow-bar linked to the trailer inside.
There's no aerodynamic drag, only rolling resistance ( RR ).
The rig is accelerated up to the test velocity, then the tow-bar is 'released', transferring all the RR load onto a strain-gauge load cell, or 'spring scale' measuring device ( like a fish scale ).
The observed load is divided by the all-up weight of the test vehicle, and the RR force coefficient ( Cfrr ) for the set of four tires falls out. Dividing by four gives the individual tire Cfrr.
Coastdown testing would spit out the value as well, but I can't recommend it. It's not for amateurs.