It depends on what paste mix you are using. I use Swim Stim groundbait to make my paste and by adjusting the amount of water you can get a really stiff paste which will mould round a pellet and survive a not too vigorous cast on a method feeder. I used some SuperG (green) groundbait last week and found it maste a very sticky mix which would work well on the feeder.
Not sure how long they will last in the water before dissolving. Never had to do this myself but if you want a solid mix for really long lasting effect then I presume that a small amount of PV1 binder or even some white crumb or ground vitalin mixed in to your dry paste mix would work, but be careful as the paste could end up like concrete.