Yeah. WD40, PB Blaster, or something like a really light 3-in-1 oil should work. Just spray it on and let it sit overnight and they should come out.
Prevent it in the future by buying some high-temp anti-seize compound (usually found in the adhesive/silicone aisle at the parts store) and putting a very light coat on the threads before putting the new ones in. Its basically grease that won't melt or degrade over time, so 60k miles later, they'll screw out just as easily as they went in.