Todd, you could use a Dremel with one of their milling bits to rough the bottom out, then use one of their sanding drums to finish. Use slower speed with fine/medium grit so as to not burn the plastic. Estimated time- 15-20 minutes.
Another idea for getting an authentic appearance on turbine exhaust duct would be to wrap with MonoKote- you can get it online at major hobby sources, or Amazon. You can get it in chrome or brushed metal finish. Easy to work with, heat shrink vinyl wrap.
Your wife's or girlfriend's hair dryer will work fine. Cost- approx. $15-$20.
Amazon does have an off brand variant called Oracover (by OraCal, a high quality vinyl graphics vendor) that is equally as good for approx. 1/3 the price of Top Flite MonoKote.