If you have any of the large hairy green mushrooms, they will feed on larger particles of food, like mysid shrimp. If these are what you are talking about, then just squirt food towards them and they will fold up around the food and look like an onion bulb until it's gone. Other mushrooms you don't really have to "target feed", even the large green mushrooms mentioned above don't have to be target fed, if you feed your reef well, they should get what they need.
Cheryl