Wheel Building - Double Snowflake

Afternoon ladies and gentlemen!
Hoping someone can point me in the right direction here - Ted, if you read this, i no longer have your number or Tom's so couldnt give you a buzz!

I am looking at building up a set of double snowflake or "flower" wheels.
Now, before i continue, yes i know it will cause the wheel to be super weak, prone to spokes snapping, going out of true all the time.....blah blah....i know.....
Im after some helpful advice and no bitching about the above points.
I work in a bike shop, im not bothered about stuff breaking...

Hubs - Condor Uno Black Hubs 32h
Rims - HP Deep V Black

Ok, so this is the pattern i am after;

Ive built maybe 40 standard 3x with a single or double "full twist" at the 3rd "x" with no problems, and never had anyone come back saying the wheels were out of true or problems bedding in. There are techniques for "pre-bedding" the spokes....

Now my problem is, i can not figure out the spoke length for my wheel build.
Standard 'flake is pretty easy, +2.5-3mm per full twist, but with this build the spokes travel aross the wheel left-right-left and right-left-right, so theres no "easy" way of guessing the length.

Second problem i found is, i can lace one side, but when i get to the other side, because the spokes arent bedded in yet and the twists havent tightened up, the spokes dont reach the nipples, and
if you add longer spokes, once tensioned up, are waaaaay too long.

So thats two issues i have found, so hopefully someone can help?

Maybe i should lace up one side, then the other with a 3x or radial for the time being, tension the spokes, loosen, remove the non 'flake side, then lace up with the new pattern, fingers crossed the other side would have bedded in by then, allowing me to use same length spokes that theoretically should now reach the nipples....

Any thoughts people?

Will buy a drink or two for whoever finds me a solution.

Cheers,
T.D