Declaring Ref Variables Inside Function Calls

[dsimcha]

At times, like when trying to write a syntactically sweet tuple unpacker, I've
wanted to be able to declare a variable that will be passed by reference to a
function inside the function call.  For example:

void doStuff(out uint num) {  // Could also be ref uint num.
    num = 666;
}

import std.stdio;

void main() {
    doStuff(uint foo);  // Declare foo as uint, passes it to doStuff.
    writeln(foo);  // Prints 666.
}

Is it feasible, at least in principle, to allow this, or would this create
issues with parsing, odd ambiguities that I haven't thought of, etc.?