The following is a quick hack to turn a directory into a TeXShop project (i.e. make all .tex files point to a single project root).
$ ls -1 *.tex | awk '{ print "/bin/echo -n \"main.tex\" > " $1 "shop" }' | sh
to check for sanity you might want to run first without the sh
pipe at the end.
This basic recipe has been turned into a more robust script in github: mkshop.