Bit late to the party ad it looks like you are going electric. We made a paddock starter for the RD 700 using a 6.5 HP go kart motor with integral centrifugal clutch, a go cart wheel and a cheepy sack barrow for the handle and wheels.
It would work better with a slick on the go kart wheel but we didn't have one.
The front roller is a conveyor belt roller modified, the distance between the roller and drive wheel is adjustable to suit different wheel diameters.
The drill for staring from cold is:
Put rear wheel in starter.
Chock platform wheel level
with bike in neutral start donkey motor and turn over gearbox to warm oil for about 5 mins.
Put bike in 3rd, rider on bike assistant revs donkey motor and watches riders left hand, when he dumps the clutch assistant puts full body weight on rear of platform.
Bike usually starts first run.
Problems happen with wet rear tyre but extra weight on platform at the right time fixes this. The timing of the weight application is crucial and dont forget to turn the kill switch on. (surprising how often that happens )