no clue as never done the grp, but some ideas:

i assume you want to be using woven carbon tubes to come up with a light paddle.
so one possibility is to take 4' of alum tubing and shape it to the paddle and loom dimensions you desire using foam or bondo for the hand position or just squeezing in a vice to get the oval(thats what i do on both sides). (if you want orientation, the ovalization has to be on only one side of the shaft of the 'control' hand. if you consider both hands control hands(i do even w/ feather), do both but don't necessarily get the orientation immediately if cant see).

for the blade side, i use 4 or 5 u-bolts thru a 2"x1"x3' metal channel as a backer and pound the alum shaft to the shape i want. pound mainly on one side if scoop blades are desired or flip back and forth if not. forget if insertion not desired.

if just alum shaft paddles desired, form on the blade.

if want the carbon shaft, possibly one way is to wax and pva the alum shaft and then put all your old glass strips on it to make a flanged female mould of the shaft, maybe glass on a foam rod or 2 for linear stiffness. split the mould, thread the carbon on some masked surgical tubing, wet out,clamp the mold halves(they should have say a 1/16" diam perforation every 4 or 6 inches ) and blow up the surgical rubber with the garden hose or tire pump. after all the squeezeout is cleaned up let sit until cured. release pressure. one issue is how far into the paddle blade(and on which side) you wish the loom structure to insert. and the fundamental one is how straight the loom ends up, hopefully the use of the alum will do this.

I wonder if the other idea with foam needs an internal tension line to keep a straight member,

or a partial female mould w/ the ctr cut out, foam to a crank angle if you desire, remould the ctr section and form as before with pressure to achieve c/f cranked looms.
could choose one pc also.

split and scrape up the seam line. might have to make a judgement abt how long the rubber should be to achieve a flat paddle end. or just clean up the end before blade forming.

anyway might work
-mick