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I'm fairly sure the answer is "No", but you can add one. I bought a Ford Accessory kit which is no longer available, but some have just cut the plenum and added it; check the Heating and A/C Forum.
They don't come with one - its a dealer installed option. If you want to add one, just buy a filter and cut the slit out in your heater box under the RH side of the dash. Its a slit the same shape as the filter - check under there you cant miss it. Real thin plastic - I poked a pocket screwdriver through mine and then worked the screwdriver around the door until the plastic popped out and just insert your filter.
Well it only takes about 10 minutes once you get it figured out. As far as is it worth it, you take the old filter out after about 12,000 miles and you'll say yes definately. As far as can you tell its in there, IMHO no.