I'd suggest instead of moving the party platform to the right you should do what the PA Democratic party has done for years, which is tolerate and support candidates who don't always agree with the party platform. The Caseys are hardly social liberals, but the state party backs them.
The Republicans win because they have a big tent. Lincoln Chafee, Arlen Specter, Olympia Snowe, Susan Collins, John McCain, and hopefully soon Tom Keane, Jr all find a home as Republican Senators. Its a very big tent when Lincoln Chafee and Tom Coburn are both under it.
The Democrats on the other hand have Ben Nelson.... uh.... Ben Nelson, and Ben Nelson. Smaller tent. This is what I'd work on if I were a Democrat.
The Senate Minority Leader is pro-life. Would the Republicasn ever have a pro-choice caucus leader?