We worm individual birds with Flubenvet mixed with Olive oil. The 1% scoop of 6g is sufficient for two large fowl for 7 days and mixes OK with 15mL, so is given as a 1mL 'shot' when the bird has a full crop. Two problems though are mixing it, as it rapidly drops out of suspension and major risk of the bird inhaling it and choking. So essentially it's not a procedure I'd recommend for regular use but can be used in an emergency if the bird is ill and not eating treated pellets.
We have found that the first or second day's shot is sufficient to kill any worms so we now administer just 3 shots on days 1, 2 and 7 (to kill hatched eggs). We also use the 2.5% Flubenvet which reduces the amount to administer to 0.5mL and reduces the risk of choking.