maybe a templedog on a small plastic tube with a single hook would work. If it didn't work then at least you would still have it in your box for salmon.
Oh, it would work!!!!
Sorry if I offend anyone, but Rainbows, especially at this time of year, are not the gentle, dellicate mythical beasts that gently sip in tiny Caenis, bearly making a ripple..... they are infact highly effictive predators capable of taking VERY large items if they want. We have taken them, with regularity, on whole mackeral, whole sardines (a favourite rainbow bait of mine), large lures when trolling for Pike and Ferox (10" plus plugs), jerk baits, soft plastics, huge flies, and in days gone by before I stopped using livebaits, live 6 -8oz rainbows!! (ps. Livebaiting is banned in scotland now, and i support this).
On a Pike day on Menteith two weekends ago, there were 11 rainbows landed and safely returned by the lure guys. The rules state lures must be 8" and above..so it gives you an idea of the vorocity of which the Bows were feeding.
On the day, rainbows will not shy away from very large flies indeed