I can't say I agree with "it-was-worth-a-shot," but I certainly agree with "trash bin." Sorry, I'm terrible on toes - I seem to step on them all the time...
On a model your size - it's possible to pull off what you were trying, but the complications of supporting the mast without interfering with their rotation can get more complicated than just bracing the yards outright.
I've found that the best way is almost always the way it was actually done and working on Constellation
reinforces that with every part of her I start to work on. The trick part is scaling it down. In my case I want it to look real too - but that's me - you can often adapt the function without needing to adapt the appearance.
Look through the SC&H Brig thread
and you'll find more useful information on bracing the yards than you can imagine. A great deal of learning was posted in that thread - foot prints in the mine field for you to safely follow.
The attached images are from The Radio Controller Square Riggers Catalog
and demonstrate what's probably your best bet for the Beagle
BTW: if you use a pointed soldering iron to make any holes you need in the Supplex, you'll get a "grommet" that's less likely to fray or tear as the heat melts the cloth around the hole.