Including files from outside the TEMPLATEPATH

So here’s the question. I’m in the process of developing a large site, and a number of other pages I use all utilize either php or html includes in the sidebars on the pages. I’d really prefer not to have to put these files in each theme as I will need to build multiple themes, and duplicating files doesn’t make any sense.

Is there any way to include files into your theme from outside the TEMPLATEPATH?