What you are proposing is likely impossible because VST is a streaming interface.
Here's an excerpt from a blog post where I explained a similar issue where people were asking why they couldn't have a real-time paulstretch VST:
I’ve seen a few people ask why there isn’t a real-time version of
Paulstretch e.g. as a VST or AU. This proved to be more difficult to
explain to people than I expected as most people seem to think the
problem is a performance issue.
Even if you had a computer capable of running it in real-time, a
Paulstretch DAW plugin is not possible for the following reasons:
An audio plugin (e.g. VST) streams audio from inputs (e.g. a vocal)
through onward to the mixer. Inherent in that premise is the
requirement that the plugin processes a block of audio input into an
equally sized block of audio output; you can’t have the playback
position moving slower for some tracks than others or the whole band
would get out of step.
Paulstretch, on the other hand, is designed to output more audio than
it inputs – that’s kinda the point of it. It could not be turned into
a VST because it doesn’t fit the problem they solve.
Companies like Melodyne have also had issues with this (they want access to the vocal tracks before they are played), they have created technologies like ARA
As far as I can tell this is just another integration point into the DAW.
I know Reaper has a very comprehensive API that might be thought of as a Macro on steroids. Perhaps that could achieve what you need? http://www.cockos.com/reaper/sdk/reascript/reascript.php