if you make your own boilies, just don't roll all your mix leave a bit to one side and use that.
if not there's 2 options.
either get some base mix of the same type as your boilies and all the flavours the expensive option or
get some ground pellet( halibut or trout)
beat an egg, add a bit of flavour then knead in the pellet powder untill it becomes as stiff as you want it. the cheap option.