You should try making up some adjustables yourself. It's very easy using the Clamcleat details in the following links.
I recently purchased two at our local Whitworths boat shop for $51. Previously I'd used simple plastic 'ladder locks' & 25mm wide webbing straps, and while they worked ok shortening the harness whilst hooked in, it was a little awkward doing the opposite. With the roller Clamcleats its effortless to control the line length either way, no matter your load on the line. I find making a loop at the end of the control line allows one to grab it with the fingers only and adjust with ease. Set them up so when the control line is fully in you are at your minimum and when the control line is fully out (the loop end is stopped by the cleat) you are at your maximum. Overall it will help your sail trimming up & down wind as well in different strength winds. I can't sail a board, any length board for that matter, without it having adjustable harness lines.
http://www.clamcleat.com/marketing/news_article.asp?theid=1063clamcleat.com/cleats/cleat_details.asp?goac=true&theid2=72