I think that most parties you encounter will not and do not require continuous healing. There will be moments when you will be waiting for enough damage to be worth a heal. In those moments, cast Broil/Ruin/Art of War.

That is all that is being asked of you, to be doing something useful as much as you can.

If you are physically incapable of having enough key binds for 2 DPS skills, then explain that. Some people will still be jerks, but hopefully most will have some understanding.