Gem dependency / installing multiple gem from a single file

Ruby gems has a nice way of defining and including dependencies but it
does
not work when some of the dependent gems are not available from download
server.

So as an example I want to distribute a gem that depends on some gems
that
are not owned by me and not available from a download site(s). Can I
create
a “uber” gem (maybe a zip file) that contains all the gems that I need
and
then make that super gem file available for download?

Thanks
Nasir