Tilly used to do that and we changed her onto different food that had larger pieces that she has to chew which slows her down.  Another idea would be to put their feed in a kong so that it is then an activity.

You could try filling a Kong with some of the food and placing it in the food bowl. Not only will Wilma have to slow down to eat the food around the Kong but she'll also take awhile to get the food out of the Kong.

Tennis balls... that might work. Actually, I forgot to mention above how I deal with Bonnie's greed: I feed her twice daily, so that she can only wolf down half the amount in one go. She used gulp down the lot and then walk around visibly struggling to breathe.

Don,t know if this will help, but when we first got Sasha as a companion for Cas, Cas would wolf done her food as if she was back on the streets as a stray(god only knows what she went through) any way we decide to try ad-lib feeding anyway it seem to work for her and she does not scoff like she used too. When we first got her she was the same but at that time we had a regime that the humans ate first then her, I would fill her bowl and then pretend to eat from it give her a few bits by hand then give her the bowl, interupt her half way through and then do the same again. It is a sharing thing which they must learn much the same as in the pack i.e the Alpha leader. Nora