Bad idea? Good idea? Over-thinking it?
Pre-drawing combs for a Warre using a conventional hive is not just a good idea, it's by far the most sensible method of transferring a colony.
I did just that - using 'Delon' wire frames tie-wrapped underneath conventional frames, rather than plain top bars - but the principle is exactly the same. I chequer-boarded 8 of these into the brood boxes of several hives spread around the apiary, and when they were 70% or so drawn (several had brood by this time), pulled them out, shook the bees off, and inserted them into the upper of 2 Warre boxes, with undrawn 'frames' in the lower box.
Then I simply shook the colony of choice from it's conventional hive straight into the Warre - leaving the Warre boxes in the old hive's place, to pick-up the foragers - and walked away. It really is that simple.
No perching a conventional box over a Warre box and hoping the bees will work their way downwards - no introducing a shook swarm and hoping they won't abscond - or any of the more uncertain methods advocated by Warre enthusiasts.
Nuts for wanting to try a Warre ?
It's a different style of beekeeping all together - far more 'leave-alone' than conventional hives - for example: pulling top-bars is difficult (combs require cutting away at the sides etc) - but if you stick more-or-less to Warre's philosophy of 2 inspections a year, then they work fine. The bees love 'em.
But - if you try to run them like conventional hives, then they're a pain in the backside. (imo, of course)
LJ