He remained out of a Champ Car ride until he replaced an injured Tristan Gommendy at PKV Racing at the Rexall Grand Prix of Edmonton.

The following week at the San Jose Grand Prix, he signed on with Pacific Coast Motorsports to fill in for Ryan Dalziel, who was injured in a bicycling accident.

But at the Belgian Grand Prix at Zolder, Mario was again called on as a substitute after Dan Clarke of Minardi Team USA was suspended for the weekend after causing a multi-car crash in a practice session.In 2008, Dominguez announced that he would enter the remainder of the 2008 IndyCar Series season with Pacific Coast Motorsports, after placing third in the final Champ Car race at Long Beach.

Since his 21st-place finish at Texas Motor Speedway in June, Dominguez's team skipped the next events to re-evaluate their program to be more competitive when they return.

This will not be his first sportscar events, since he did a couple for a Risi Competizione American Le Mans Series team in 2006, delivering good results.