Running out of space

Hi,

After a year or so of xbmc usage I am currently running out of space on my 30 gig SSD.

Majority of the space is being taken up by:

User Data->Thumbnails (4 gigs)
and
User Data->addon_data->script.artistslideshow (4 gigs).

Is there a way to specify where these thumbnails/images are stored? This way I could move them to an external HD that I have attached.

Thanks