Grease on the base gasket seems to help soften it. When you torque down the head studs that gasket will compress, conforming to any minuscule irregularities. If there's any oil seepage after doing this, look for other issues.
I've also used a very thin coat of Gasket Eliminator (made by Loc-tite I think) without problems, it is made to seal small gaps (up to .015") but be careful around your oil supply holes, let the O rings do their job. I coat all cover gaskets with this stuff - it does eliminate oil leaks.
DON'T USE any product like Yamabond! I saw saw the aftermath of this once, the guy ended up with broken fins trying to get the block off the case, and his covers were stuck on so hard he had to hammer them off.
I have used copper coat on head gaskets without issues, head removal and clean up was easier than a dry installation.
And if you don't already know this, I would strongly advise against using any kind of power-driven Scotch brite abrasive wheel to remove or clean up any old gasket material from aluminum. My buddie's machine shop does a good business resurfacing aluminum heads that won't seal after a Do-It-Yourselfer gets done with his Dotco and 2" discs...