There are two approaches (at least) to think about. One is to treat the contracture. The other is to make the guitar easier to play. Ideas on that:

Make sure the guitar is set up right, with strings not too high.

Try a narrower neck.

Are you holding it right?

Switch from high tension to medium tension strings. (or would it be the other way?)

Frets can be higher or wider than usual. Both mean that it's easier to play.

Here's the URL for a Gibson site that talks about frets. Interesting stuff!

http://www2.gibson.com/News-Lifestyle/Features/en-us/10-things-you-should-know-about-frets-0705-1.aspx

Take a break between songs, and rest your hand.

Stop smoking. It says so on the page linked above.