There might be more elegant ways to do it, but this is what I did:
-Open GEdit or other text editor
-Type in "optirun [or primusrun] java -jar '[directory of launcher jar, IE "/home/[user]/downloads/minecraft.jar"]"
-save the file as "Minecraft.sh", to make it an executable script
-right-click the file, go to properties > permissions > check the "allow executing this file as a program"
Now you should be able to right-click the file and click run. I know there's an option in the file manager properties to make the file execute on double-click, but I'm on Kubuntu, and it's a bit different. I don't remember how to change that option it on regular Ubuntu, sorry.
Also, protip, if you're not already using it, use Primusrun instead of Optirun with bumblebee. if primusrun isn't installed, it's just "sudo apt-get install primus". I've noticed some pretty definite speed boosts with it.