Lateral balancing
If you are that concerned, you could arrange to have a pivot point under the nose instead of using the engine. But unless you're flying Pattern or Competition Aerobatics, you'll never know the difference.
Consider this, you put weights on the wingtip to balance it, then glue them in. The glue has weight too. What I usually do is to use small "SplitShot" fishing weights. Once I find out how many I need, I remove 1 to allow for the weight of the glue (and at that, I think I'm being a little anal)
The bottom line is - It doesn't have to be perfect, just as long as it's close.