Decided this game has slightly dated input functionality, and decided to make a small Autohotkey script for it.

The script binds:
Scroll up to Page down
Scroll down to Page up
Middle mouse button to Enter

Make sure that the zoom in, zoom out and rotate keys are set to their defaults. Enjoy!

dl.dropboxusercontent.com/u/24882205/useful_shit/RCT-Keys/RCT-Keys.rar
dl.dropboxusercontent.com/u/24882205/useful_shit/RCT-Keys/RCT-Keys.ahk

I couldn't post the links because my rep is too low, so please vote up and I'll update the post.

Use 'X-Mouse Button Control': https://www.highrez.co.uk/downloads/xmousebuttoncontrol.htm - to easily map the mouse wheel and buttons to what you please. I mapped my mouse whell to PageUP and PageDown, and set these keys in the game to zoom in and out, respectively, and now I have mouse controlled zooming! I also mapped my mouse wheel (button) press to HOME and use that to rotate the game map.