Jed Babbin is offering some very sage advice to McCain, I hope he takes it:

According to my source, McCain has prepared a video featuring President Ronald Reagan to make the introduction. If McCain uses this video, it is very likely to backfire badly. This is the group before which Ronald Reagan said in 1975 that, “A political party cannot be all things to all people. It must represent certain fundamental beliefs which must not be compromised to political expediency or simply to swell its numbers.”
Very few of the 2008 CPAC crowd will see McCain as the successor to Reagan and Reagan’s principles. McCain has sacrificed conservatives’ fundamental beliefs throughout his Senate career. If McCain uses this introduction, the boos will be very loud.
[…]
First, he could throw away the Reagan video introduction. If he uses it at CPAC — a house that Reagan built — he could alienate a large portion of the conservatives he needs.
Second, he could say a lot more than he has so far on three key issues: Supreme Court appointments, the war and illegal immigration.

Read the details here.
I would add that he should leave his arrogance at home and not try to convince them that they’re wrong about him, he really is a conservative. He should not be dismissive of their concerns but he should be honest about the differences and emphasize where their concerns and his concerns overlap. Focusing on the issues that Babbin suggests would give him common ground with conservatives and would help them to accept his candidacy more than if he came there with a film that told them who Reagan was and how McCain is able to carry the Reagan mantle. He’s not and he shouldn’t lie about it. That would cause a further rift.
What McCain and others should understand is that Reagan conservatives believe in the principles that Reagan governed by, not because Reagan governed that way but because we believe that is the way this nation should be governed. McCain does not believe in these principles, if he did he wouldn’t have introduced McCain-Feingold, he wouldn’t have voted against drilling for oil in ANWR, he wouldn’t have voted against the Bush tax cuts, he wouldn’t have introduced McCain-Lieberman or McCain-Kennedy, etc. He should be honest about his principles for leading this nation and demonstrate where they overlap with the principles of Reagan: a strong military and fiscal discipline.

A promise to run on these issues (and not global warming or closing GITMO), to run as a deficit hawk, as someone who wants to strengthen our economy with incentive tax cuts, a commander in chief who will spend the money necessary to strengthen our military as we prepare to meet our future enemies and as someone who isn’t afraid of taking on the promises of both Obama and Clinton to raise taxes if elected. If he can convince conservatives of this, he may have their support in November.
Conservatives at CPAC should remind him that he needs them in November (the Democrats will already have a liberal that intend to vote for, they don’t need another) and his outreach shouldn’t just be limited to one speech. They should let him know that how he runs his campaign in the general will affect how many of us turn out to vote. And it would be very helpful if someone would tell him to stop attacking conservatives and turn his attention to the Democrats.