Right now relative humidity here is 79%. No sparks now!
I like the solution (!) proposed by Brendan, EI6IZ:
You can get an anti-static spray designed to treat carpet, upholstered furniture etc. This is a sensible thing to do if one tinkers with electronics and for the average hamshack a bottle will last for many years as it only needs to be applied lightly and infrequently.
For example http://ie.rs-online.com/web/p/esd-safe-clean-room-treatments-lotions-dispensers/0182893/ For cheapskates however, diluted fabric softener sprayed on the carpet and chair will work well for at least a few months but will require much more frequent application than the 'proper stuff'.
I give my car seat an occasional squirt in dry summers to stop the 'zap' when getting out on a dry day.