I use Cytomic's "The Drop" effect for filtering, and it has a cool feature whereby you can trigger its filter envelope via a MIDI input. So this seems like a good idea in cases where you're not happy with the filter on a synth and would like to use one of The Drop's excellent filters instead. The MIDI being used to play the synth could used to "play" The Drop. However I'm confused as to how I should go about setting this up in Sonar. You cannot give a MIDI track any more than one output so how would I get that MIDI to The Drop as well as the synth? It's not as if we have MIDI sends (although that would be great!). 
 
So they only way I can think of doing it is by duplicating the MIDI track and giving The Drop its own copy. However this would be a pain should you ever need to make edits in the original MIDI. I thought about cloning the track and selecting "link to original clips," but this doesn't appear to keep the tracks truly linked, i.e. any edits made are updated in linked clips, but the linked clips aren't linked by location, i.e. if you move a clip in the original track, the linked clip stays where it is. Not ideal in the slightest. 
 
So I'm hoping there's just some hysterically simple way of doing this that I'm too much of a dumbass to work out? 

Unfortunately, at this time, there is no way to do what you have described.  A MIDI send function would indeed an excellent way to do this.  This feature has been requested.

http://forum.cakewalk.com/FindPost/3156179

Lots of folks work around this using the free LoopBe virtual MIDI cable to send and return the MIDI from one track back into SONAR as a MIDI port that can be assigned as input to multiple synths.

If I get what you are trying to do you're talking about a MIDI sidechain, is that correct?
 
If, that's the case it can be done but usually the response/routing is handled by the plugin internally. If it is capable of doing that an extra MIDI track is needed with input from the controlling plug and output to the target plug. If using an audio FX it'll probably need configuring as a synth.
 
I've certainly done similar with Blue Cat plugins but they are designed to handle the MIDI data internally to do that and I'm not familiar with "The Drop" so have no idea whether the method I have used will work with that.