how are you planning to run your ruby scripts? via Ti.Process? Otherwise, the TideSDK ruby module is what it is - there's no different versions you can use with rvm (Afaik).
Update/Expanded: I should point out TideSDK bundles its own Ruby - its not using the system ruby.
Otherwise, you can execute ruby scripts via Ti.Process (like any other script you would execute from the CLI). So, in your script, instead of #!/usr/bin/ruby
you could do #!/usr/bin/env ruby
. Of course, this wouldn't be very portable if you relying on rvm on target systems, but if you are doing a limited ditrib to known targets (ie: internally where you know everyone has a system setup with rvm) you could probably get something working.