I get the safety factor if you're going offshore, but wouldn't think you would need it for trolling, that 50 should troll sweet all on its own. If it's too fast, you could swap the prop down one size, just watch your rpms when running at full throttle.
If you really want the kicker then you might have no choice but to use a bracket. Just screwing it on as is or putting a filler strip on top of the transom isn't going to be secure enough, you risk losing the motor if you bump around in chop when running with the big engine. You could make a cut out in the deck so you can drop it to the correct height, but before you cut anything make sure you still have enough room to tighten the clamp screws. You might also want to email Lowe or talk to the dealer first and make sure there's nothing under there to cut away by accident, like transom supports, live well plumbing, etc.
Also watch the weight on your transom. The 4.5 will probably be ok but some of the four stroke 9.9s are over 100 pounds. That's pushing it.
Personally, I wouldn't bother. If you're seriously worried about safety just get a handheld VHF radio and carry another battery for your electric.