I'm not sure Gnome launcher supports this, but in a bash script a command like
means - start program1, then start program2 only after the first one terminates.
After some testing I think the most robust thing would be to create a simple script:
rvm use 1.9.2 &
set the executable bit on it and then create a launcher which starts this script, i.e. /home/yourusername/start_redcar.sh
As a bonus - if you create a directory called "bin" in your home folder, put the script there and name it "start_redcar", you'll be able to start it from terminal or from the "Run a command" window which opens when pressing Alt-F2 - by simply typing the command name