One thing that might help is an internal spoke wrench (not sure the technical term), they are designed to work from the inside of the rim, so you need to have your tires off. They are like a screw driver but with a pin that you insert into the head of the nipple and as you twist it, the spoke will push it out and all your spokes will be at the same tension.
From there you can go through and tighten them a little more if you like, just make sure you give every spike the same twist, 1/4 turn for example. The picture here looks like it was home made, and you could do something similar on your own with a screwdriver and a file.
This might not get you the "proper" tension, but it will give you even tension. With out a torque wrench, you just have to learn the tension by hand. I listen for the "pop" and gauge off of that.