Conditional gem dependencies
Hmm,
I believe one can code multiple dependencies because I've noticed gems which seemed to do this. But I would you advise against doing this. No matter how simple the code you are inserting here is, when you consider that the user will be loading one gem which depends on another which depends on another, even a small glitch in the logic of one piece of code or another can make the whole dependency train a nightmare.
So, I'd leave your kludge as-is. Further, I'd suggest you have a tarball that users can download as well. I've had to manually extract the code inside of gems whose configuration code wouldn't let me install them.
checkout a somewhat tutorial here: https://github.com/rdp/ruby_tutorials_core/wiki/gem (https://en.wikibooks.org/wiki/Ruby_Programming/RubyGems)
it shows how to install different versions of dependencies depending on what version of ruby the installee is using.
(short answer--it ain't as easy as it should be)