registering gem dependency within plugin?

Rails Gurus --
In 2.1, is there a way to get a plugin to register a gem as a
dependency. I was unable to get this working from the plugin's
init.rb-- it seems that it is read in too late in the init process?
Is there something I'm missing?
Thanks for the help! (and thanks as always for the best webdev
environment ever!)

thorny_sun