This is definitely viable option to use second saber, verified by centuries of sword&buckler and rapier&dagger pairs
Consider your weapon in second hand as a shield and you will be able to build real combat skills.
Another option to consider is to block with both weapons, keep secondary weapon to block and control opponents lightsaber, free your primary weapon and strike opponent, pretty safe play
I second this. the off hand being a shorter weapon, and primarily used to block is classic. Not that this style was prominant in the era of rapiers. light blades, not heavier longswords. attacking and blocking is much more nuanced.
Additionally, if you are both right handed, the attack will come from your left, you block with your off-hand tying up their blade, and your dominant hand (the right) is free and clear to kill.