You will be better off if you can scrape the mulch away from the plant (with a hand cultivator), put down the fertilizer, scratch it in (again, with the hand cultivator), and pull the mulch back over the dirt. If you have a ton of bushes to do this to, I would guess that you could put the fertilizer right over the mulch, stir the mulch around a little, so the fertilizer gets off the top, and water it in. Or, as you say, use liquid fertilizer.

Joan

Yes! You can simply spread the fertilizer over the mulch.