Short answer: No. Long answer: possibly - how much time have you got?
Firstly, you'd have to make sure that the route didn't use any BVE4 specific objects - as far as I'm aware, .x format objects don't work in BVE 2. So, for example, you won't get ECML to work properly, because it contains a high proportion of .x files for signals and other objects (track, walls, signs, etc). So, if the route doesn't use .x files (or if you've got time to make your own replacements), you'd then have to go through the route file removing all BVE 4 -specific commands (mainly beacons for things like rain). Then, you'd need to go through the route file and change all the signalling commands to BVE 2 signalling commands - I believe they use a different syntax. You would also need to check all the .sta station commands, too... and this "to do" list probably isn't complete.....
That's why ECML is only available for BVE 4 - I'm afraid life's too short to build a BVE 2 version as well.
When the openBVE project is finished, you should be able to run BVE 4 routes on it - but probably without the "external" view of the train (unless developers make them!).
Regards
eezypeazy