Kissing gouramies also much appreciate vegetable-based foods and a high-veggie diet. You can try them on blanched zuchinni, cucumber or deshelled green peas. Having said that, they tend to go for aquarium plants even more readily.
If they still don't seem interested, try some live brine shrimp or bloodworm.
Also note that kissers get quite large (10" isn't uncommon) and can be aggressive towards each other - particularly if kept as a pair. Their name 'kissing' gourami comes from what they do when fighting (that is lock mouths like cichlids do). You may be aware of this already but just a heads up in case your tank is not large enough.