I'm curious what your goal is here. I know you said you want to troll. I know that there are a large number of folks out there that are interested in doing this for a variety of reasons. I see the two most popular reasons being 1) Trolling and 2) Secondary/'get-home' engine. I mean NO offense in this, but to to me this looks a bit like 'hole in the bucket' scenario, where seeking to solve problem one, leads to problem 2, and so on.
I'd be concerned about things like beign able to adequately control the boat. either you're out on the swim platform steering and controlling throttle, which sounds like you will have a 'line of sight' issue. OR, you are trying to steer at the helm using the outdrive and have no ability to control Fwd/ Revers or throttle. In order to do the latter, would then require that you run out onto the swim platform, temporarily operating without nobody at the helm. Once on the platform, one slip and you now have a vessel under power with a MOB situation. This would also give you limited control and responsiveness since you're not actually steering with the drive providing power.
I honestly don't like this from any perspective other than you can use less fuel trolling with a small outboard. The question is, how much less fuel? Is it really worth it? Unfortunately, boating is an excercise in compromise. Express cruisers make poor fishing boats, and fishing boats, typically make poor cruisers (unless you start getting into LARGE sportfisher's). Either can get the other job done, with some compromise.