I agree - rideshare or taxi will be the most practical. Using Disney transportation, you'd be looking at bus from VGF to DHS, then Skyliner DHS to CBR, then transfer to the Epcot Skyliner to Riviera. IF DHS opens at 8:00 that day, then early entry would be at 7:30 and transportation would start running around 6:30, so you might make it. But if DHS opens at 9:00 that day, EE would be at 8:30, and transportation wouldn't even start until 7:30. I'd plan on rideshare (Uber, Lyft, Minnie Van) or taxi.