Not sure how much is involved for a refund or if it is even worth it, sounds like you have to jump through a lot of hoops, but who knows...
Recreational boaters who purchase taxed fuel for use in their boats may be able to get a refund of all or part of that 'highway use tax' depending on the state in which the fuel was purchased.
According to the Federal Highway Administration, almost 4 million gallons of gasoline were used for non-highway purposes in 2001. Of this, almost 25% (993,837 gallons) was used in marine activities. The cost of this fuel generally includes a highway use tax of anywhere from 7.5¢/gallon to close to 30¢/gallon depending on the state.
Many states apply the tax on marine fuel towards boating programs through the Aquatic Resources Trust Fund. But in other states the money does not get funneled into the marine community, and instead is put into the highway improvement fund. Since boats don't cause wear and tear on the highways, bridges, and ferries that benefit from that fund, applying marine fuel tax towards the highway improvement fund is widely viewed as unfair.
http://www.americanboating.org/fueltax.asp