Zum, the 2 fly types that come to mind for me when thinking "flukes" is a Seaducer, and a rabbit strip eel. The primary problem is the fur & feathers have far more motion to them than plastic, so you can get a very active fly, with similar movement, but not exactly the same.
A heavily hackled Seaducer, with no additional weight added can be used near the surface, but it would sink at an extremely slow rate, if you needed to get it down some. Something that's much easier to do with plastic baits. This type of fly tied with long saddle hackle in the tail would be close to using a fluke.
The rabbit strip type flies also have a lot of motion, and can be made quite long.
(I use up to 14" fluke type lures for Striped bass). I've tied such flies up to about 10" in length, but 5 to 8" length is easier to cast, particularly after they get wet.
I also use a 10 wt for this type of fly.
Either of these could work. However, if you wish to use them as a topwater, a head of some type would be needed. Think in terms of "Bob's Bangers", ( Bob Popovics) with a removable foam or cork head. A variety of heads ( diameter & length) would allow for adjusting to get the action the way you want it.
I've done similar with foam cylinders, sold for fly tying, and with wine bottle corks or larger bottle stoppers. Foam works the best, but cork can be obtained cheap sometimes.