Installing a gem not hosted by rubygems.org - simplest way?

Hello.

I have a few gems that are not on rubygems.org, mostly because there
already exists a gem with the very same name. For instance:

http://shevegen.square7.ch/configuration-1.0.19.gem

Now, people can wget it, then install it, which works fine. But it
is a bit of a hassle in that you need to do two commands.

I think you can do “gem sources -a” to add more sources, but
this is also a bit cumbersome.

My question is - is there a way to install a remote gem with
just a single gem-command instruction, if it is NOT on rubygems.org?

It’s ok if some extra switches are used for this gem install command
but I am wondering if this functionality is available; and if not,
whether it may be useful to have it. If so then I may file an issue
request but I first have to find out whether it is possible or not.

Thanks!