You could transplant a standard Uruk head/helmet, either plastic from a spare figure or the metal head from the conversion sprue. I'm positive there are one or two scouts in the film with that helmet.
You could also convert said scout into a 2 handed axeman(?) by using a spare weapon or scratching one with some brass rod and a carved plasticard blade.
Assuming you are using a plastic figure then plastic glue, a sharp scalpel, a rat tail file and probaly some modelling putty ie green or grey stuff, should cover the tools needed.
hth
Greg
ps speaking of converting Uruk scouts, has anyone noticed the guy with the pike? He appears in TTT, on one of those shots filmed from above and behind the uruk 'column' as they leg it across Rohan, Bottom left of the screen from memory. It should be a nice, easy conversion that I've been to lazy to do as yet