for this sort of thing (big value treats over long time period), the best thing i've found to use is frozen liverwurst. i buy it, slice it and put it in a small container (the leftover cream cheese containers work GREAT for this) then put the container in the freezer. the pup gets to lick the frozen stuff for her high value treat - LOTS of treat over a long time, but not lots of calories or lots of treats in the tummy. the dogs at my house swear liverwurst pupcicles are wonderful. sometimes they will try to nibble, but given it's frozen and in a small container, it's hard to get lots of treats.
I will try this, but I myself love liverwurst. Hopefully I will not eat it all before getting to the park.
At the park today, I was about 75% successful with the whistle/treat recall. Not bad for the first time out, I think. Especially because there were easily 20 dogs there, and Kipawa is Mr. Social and has to visit with all of them.