In ruby, is it possible to specify to call another ruby script using the same ruby interpreter as the original script is being run by?

For example, if a.rb runs b.rb a couple of times, is it possible to replace

system("ruby", "b.rb", "foo", "bar")

with something like

run_ruby("b.rb", "foo", "bar")

so that if you used ruby1.9.1 a.rb on the original, ruby1.9.1 would be used on b.rb, but if you just used ruby a.rb on the original, ruby would be used on b.rb?

I'd prefer not to use shebangs, as I'd like it to be able to run on different computers, some of which don't have /usr/bin/env.

Edit: I didn't mean load or require and the like, but spawning new processes (so I can use multiple CPUs).