You don't have to substitute anything for the PB. You can just omit it. Here's one recipe written withtout it for you to compare yours to, or to use instead. If you don't want to use coconut, add a comparable amount of oats instead to make up the bulk.

NO BAKE FUDGE COOKIES

2 cups granulated sugar
1 stick (1/2 cup) butter
1/2 cup milk
4 tbsp. cocoa
1 tsp. vanilla
Pinch salt
1 cup oats
1 cup chopped nuts
1 cup coconut

Boil first 5 ingredients for 1 minute.

Remove from heat and stir in remaining ingredients.

Drop by spoonfuls onto waxed paper.