Enter Mini Burt...
Burt started life as an Formula 1 "lollipop" guy (the brave guy who holds the stop sign on a stick on pit row as the car comes hurtling toward him). He's a diorama accessory figure you buy separately for 1/43rd scale European diecast model cars.
I cut off his arms, legs and head, then put a brass wire in where his neck was so I could bend back his reattached head; ouch. Next I took a thin plastic rod and glued it over his brow and down each side of his face; were the edge of the helmet would be.
The helmet mass was filled in using a slurry of crazy glue and fiberglass micro-balloons. This mixture yields a uniform, sandable surface; it's kind of like sand castle building in miniature, only in a hurry. Once nestled in his cockpit, Mini-Burt looks quite at home peering over the nose of the bike.