I recently won the 3 day festival at Willinghurst fisheries in Surrey, fishing the Preston method mould in conjuction with sonubaits 2mm fin perfect moulded around it.

The only difference was that the hook bait was a 6mm sonu  expander (un-soaked), as the method breaks down the expander pops out of the top and is clearly visible to the carp, as another bonus the expander counters the weight of the hook so it really catches the carp of guard .
You can test in margins to gauge break down time of mould and then apply on your chosen spot, i generally give it 2 mins then recast.
Give it a try, the results are amazing!