Actually there is. Someone took a Nyko wormlight and just changed the plug to fit the GP32, although unfortunatley I don't remember the website. I think it was on GP32Emu.com, search in there if no one else knows the website. Good luck.
Sort of - someone wrote a guide to explain how to mod a worm-light for a GP32, and you can fix a few GBA accessories to it. But atm there's nothing official - hopefully by mid this year
Joecool,
Try going to my website on http://geocities.yahoo.com.br/christianobergmann/ and then click on the guide link provided in there (in the phrase "check here for a tutorial").
My server is kinda weird - but I've noticed that some links to files redirected from here don't always work - I don't know why.