How to use reflection to intercept an expression prior to evaluation?

I was hoping to use R's reflection capabilities to intercept the current expression under evaluation before it is evaluated.

For instance, to create some syntax sugar, given the following:

> Server <- setRefClass("Server",
>   methods = list(
>       handler = function(expr) submitExpressionToRemoteServer(expr)
>   )
> )
> server <- Server()
> server$foo$bar$baz    #... should be map to...    server$handler("foo$bar$baz")

I want the expression server$foo$bar$baz to be intercepted by the server$handlermethod and get mapped to server$handler("foo$bar$baz").

Note that I want this call to succeed even though server$foo is not defined: I am interested only in the expression itself (so I can do stuff with the expression), not that it evaluates to a valid local object.

Is this possible?