Tell them to donate their warchests to the DCCC or candidates who need the money.
MD-05 Hoyer $875,508
MD-07 Cummings $332,012
Also, some folks aren't running unopposed, but have no real chance of losing:
MD-02 Ruppersberger $400,266
MD-04 Wynn $206,823
Thats easily over $1,000,000 that could go to other candidates in Maryland, or to close races around the country, and the is just Maryland house candidates.
If this push for donations from unopposed candidates works, it could be a huge deal for numerous races around the country, as well as for the Democratic Party as a whole. Make those calls!