Schema.org potentialAction input constraints for complex/nested values

I'm trying to figure out the correct way to implement potentialAction input
constraints (with a templated target URI) for an Action that requires a
complex value as input. Currently, I'm referencing this
<http://schema.org/docs/actions.html> documentation.

As an example of what I'm asking, let's say I have two schema.org Place
objects (one representing a source location, the other representing a
destination location). How do I then construct a potentialAction (namely, a
TravelAction) that can be interpolated using these two Place objects as
input?

I was hoping that RFC6570 <http://www.rfcreader.com/#rfc6570> would have
some kind of syntactic allowance for "dot-notation" in order to traverse
complex values such as:

{
  "@context": "http://schema.org",
  "@type": "TravelAction",
  "target": "
http://mysite.com/travel?from={from.address.streetAddress}&to={to.address.streetAddress}
",
  "fromLocation-input": "required name=from"
  "toLocation-input": "required name=to"
}

But per the RFC, there is no such thing presently specified.

However, I have noted the following quote from the relevant Schema.org
documentation regarding the URI templating with Actions:

> The allowed references in the templates for substitution are dotted
schema paths to the filled-in properties (relative to the Action object).

The above quote very much so sounds like there actually is some proposed
method for interpolating values nested within complex objects.

Can anyone verify my assumptions? Or are is there some other sane way of
expressing this kind of input constraint for a given Action?

Thanks for any info
-- 
-jerluc