Scratch built CG question

Hello Guys, I have a scratch built design of mine, however I cannot get it to string test for proper CG (I think the fins are in the way)
any ideas? Is there a rocket out there that looks similar I can use as a guide? Its ready to go except for the finish. If all else fails I may do few test flights before painting to figure out the balance.
It can be seen here http://aileron37.blogspot.com/2010/02/scratch-built-called-trident.html
Thanks all rick
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Use a piece of string on a bit of tape. You can always add a bit of nose weight. The design looks fine though, everything is where it should be; no large canards.
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