Just place it on the dowels and stand to the side and look at it. It should sit slightly nose-down. How much? Just enough that you can see that it's not level.

Now fly it.

A roll really won't tell you if a plane is nose heavy. The two most obvious things (to me) are:

1) it won't slow down for landing

2) it won't do a spin - it will just sort of spiral down.

If it flies the way you like, leave it. If not, shift the battery, or add small amounts of weight until it does fly the way you like, but you really don't need to put it back on  the balancer - that's just to get the initial setup.