Increasing the number of themes displayed in Appearance -> Themes

Is there any bit of code, or snippet or hack that could be used to increase the number of theme thumbnails that are displayed in the dashboard on Appearance->Theme?

I'm running a multisite and have about 300 themes available - but only 15 themes are displayed giving users almost 20 pages to browse through. That's a lot of pages, I think the large number of options is good, but it seems like users aren't getting to some of the beauties that in are in there after page 10.

There must be something in the code that can be changed to increase to 30 or 40 themes per page.

I'm pretty sure that it'll really slow down the page load, so it has to be tested out a little, but I just want to know where to change it.