Could you set 'exrc' and create an appropriate vimrc in each project
directory?
You could also setup autocommands if your project files are in specific
directories.
au BufNewFile,BufRead /path/to/project1/* setl ts=4 sts=4 sw=4
au BufNewFile,BufRead /path/to/project2/* setl ts=8 sts=8 sw=8
Note that these don't have to be full paths; ie this would work:
au BufNewFile,BufRead */project1/* setl ts=8 sts=4 sw=4
au BufNewFile,BufRead */project2/* setl ts=8 sts=8 sw=8
~Matt