Why would you want to play a partial role of a Sith Warrior when your best chances of survival is to stay away from melee? As a sage you cant be effective with melee, thats not your training's purpose, not your role.
I understand you want sages to have melee attacks as well but you are not that class, you are dead weight to a team if you want to melee with a pure range force wielder class.
I don't want to come off as rude but it seems like you are missing the point.
I don't think any sorc/sage is asking to be good both in melee and at range. It's just that the lightsaber is such an integral part of both Sith and Jedi so it feels really awkward that we can't do anything with it.
It wouldn't even have to be a melee damage attack as far as I am concrned. Just an ability that required you to use the lightsaber to activate it would suffice.
I have posted this before, but say that you have Affliction up on a target and then hit him with for example Thrash. This would cause Affliction to immediately detonate for the full damage with some splash damage to neaby targets (and if they also carried Affliction those would detonate too). Obviously this would put Affliction on some cooldown to prevent chain casting.