With any combination of sabers in your hand(s), with any combination of the blades ignited, pressing 1 (or whatever other button is bound to using the saber) will more than likely shut them both off, and so sheathing both sabers. Is that not what you're asking?
If you're trying to keep the left handed saber on to attack with it while the right handed on is off? I think I did this by:
throwing the right handed saber far away
pressing 1 to sheath it which is like dropping the thrown one
then press 1, or attack I forget which, to ignite saber 2
if you press attack it will probably draw the 1st saber towards you. In this case press 1 to sheath it again maybe, I don't know? Or throw it someplace where it won't get to you, say behind a wall or off a ledge and under the floor, say in the rail sp level. Then you should be able to fight with only the 2nd blade in your hand.
And I'm OUT THIS MUFUGGA!