If airspace and cloudbase permits, climb to a higher altitude. You'd be amazed at the difference 1000' makes. You might not totally get rid of the bumps by doing this - but it'll make them less bumpy. Also look out for cumulus cloud and their dark flat bases. the thermals will be just under/just upwind of them.
Old Smokey is right though, it's not dangerous - just a little uncomfortable.
I would suggest taking a trip in a glider on a day with around 3-5/8 Cumulus cloud. It'll be bumpy - but for all the right reasons!