Is this possible?

No, not yet. The controls are fixed in the source code, hence no easy way to change them by altering Reus.

The easiest thing you can do is using 3rd party software like AutoHotKey, but I'm not sure if it's worth the effort, as I always pause the game when speed becomes critical anyway.

Reus is still under development, so they may hand key-mapping in later. But as of now, the current patch (in beta version) doesn't contain it.

To make them aware of demand, I'd just send them a short mail to "info at abbeygames dot com".

I actually didn't need it after I noticed you can move to left and right by holding down the mouse (they really should put a picture that portrays all the default mappings at least) but I found out that before I added a script with AutoHotkey and worked quite alright.