Prior to going WFP, I gave Ian_Giles 8 or 9 houses that I did trad that were located next to a field that had cows in it; which produced poo; which in turn attracted flies who pood all over the windows of these houses.
There were all detached houses with windows that had those awfull plastic strips stuck to them; to give a fake Georgian window effect.
They were awful to do trad; a real 'groaner' when they were due. I even bumped up the price because of the work involved, but met some resistance, so I dumped them on Ian.
He still does them without a problem.
My advice would be to just stick to doing them with a WFP, and if it doesn't come off, then the customer will have to live with the results.
Or, increase the price in accordance with the time and effort involved and do them trad.