I've read everything you've said and I really don't understand why you wouldn't just use actors. In terms of performance, you don't need to worry about the size of your map and how many actors will exist on it. All that matters for performance is how many actors *are currently on screen*. You can have tons of actors offscreen and it will not affect your performance too much, because Stencyl isn't drawing/updating/testing them until they are on screen. Just use actors with sensor collision shapes. You may have to make many of them, but what's the problem with that? You were going to make many tiles, too, only now they would be actors and they would mostly be offscreen at any given time, so performance shouldn't be a problem. Also, if they are actors, you can scale/tint them for more variety, thus reducing how many you need to make. I have an overworld map with just such requirements, and I have used actors to accomplish exactly what you want. It works great and performance isn't a problem because the vast majority of them are offscreen. Stencyl is at it's easiest when you use actors whenever possible.
Also -- if it were possible to have a tile with all the capabilities you are looking for, it would essentially become an actor, because tiles are basically stripped-down, barebones actors by another name. To add polygonal sensors to tiles would be to essentially turn them into normal-physics actors that can't be moved ... so just use normal-physics actors that can't be moved. It's virtually the same thing.
(If you want to scale them, make sure you set the physics to "cannot be pushed", instead of "cannot move".)
Also also -- be sure that your actors do not have the "always simulate" behavior, or they will continue to affect performance when offscreen.