(so what is a "G/W" then?)
I think I'd do either a HUGE hand-tie, one that makes your fingers hurt!! I'd go for a 'structured' look, starting with the delphs that rosa mentioned in the centre/at the top, then work my way 'down' with the flowers, clustering roses of different colours in bunches of 5 or 6 with the hydrangeas-if you have them-that rosa mentioned
inbetween the roses, the callas 'hugging' the base of the delphs, oh, don't forget something TALL and twigg-y (maybe willow?) inbetween the delphs (don't have delphs? use the lilies!stick to one colour on those tho), not too sure about those anthuriums...I always have a problem with them, they usually end up spiraling slowly around to the 'bottom' of the bq, overlapping each other...and to top it off, use LONG ivy trails 'sprouting' from it all and wound around the entire thing, held in place with aluminum wire. I think I'd finish it off with BIG leaves, got any aspidistra? Aralia? Anthurium? just plonk the big ones under it to give it a nice finish.
This is sooooo gonna make your hands hurt!!
Have fun whatever you do!
by clustering the roses you can get more 'money' in without it looking like you just threw it together!