So the summary is, the family minivan was driven "closely" behind a road patching crew for about 500ft. The result was a lot of liquid asphalt road patch on all four tires.
Upon arriving home from work I took a look and then drove the van to see if it would just fly off on the freeway, but the out of balance condition was very bad and not much flew off. I poked at the stuff on the tire and there were sections like a skim coat and others with the full tread filled plus about 3-4 mm of material beyond the tread surface. Not good. 
After much internet research and a talk with a local contractor the solution was either buy 4 new tires or use this stuff-> TARMINATOR. The issue with using a very aggressive chemical that the contractor recommended is that it would be more likely to just destroy the tire. He used his high strength stuff on metal equipment. Obviously most distributors wouldn't give me any comment on how their products would work on tires.
So I went the TARMINATOR way. I ended up only finding 2 cans before the weekend. The local NAPA said they could order me a case if needed. After all was said and done I should have ordered the case.
I found that if the patch was dry and thick (2-3 mm minimum) the chisel was the way to go. It came off in small sheets or chucks. Anything else the tarminator would help. I think the optimal would have been to put the tire into some utility tub/sink and just spray it down with the tarminator like a power washer. The tarminator did break down the patch material and basically it would flow off the tire. The issue came where the patch material combined with debris (rocks/plastic/twigs/etc) and was physically jammed into the tread grooves. So I had to use an old 1/4 wood chisel to scrape out the stuff after the tarminator.
Then immediately washed the tires. They all look clear of patch material now, just a bit sticky and no balance issues.
Took about 13 hours total.
