Follow up from IMC Club meeting:
The 'service' used to request ADS-B deviations is the "ADS-B Deviation Authorization Pre-Flight Tool (ADAPT)". It is located on FAA's "Service Availability Prediction Tool (SAPT)" website at SAPT.FAA.GOV:
https://sapt.faa.gov/default.phpThe ADAPT function (second title down) has a reasonable explanation page and a "Flight Plan" style form to enter data on a flight that will not comply with the ADS-B rule. As I said at Skylane, I believe that this is the way that the ADS-B "enforcers" will exempt a non-compliant aircraft who enters ADS-B airspace before sending any 'nasty-grams'. Of course they also track the deviations, so they don't want to see the same callsign repeatedly requesting the same deviation day after day...