Definitional Returns. Solved.

[hostilefork]

You heard it here first. The console says it all... ;-P

>> foo: func [x] [return x 20]
== make function! [[x /local return][
    return: make function! [
        ["Returns a value from a function." value [any-value!]]
        [throw/name value bind-of 'return]
    ]
    catch/name [
        return x 20
    ] bind-of 'return
]]

>> foo 10
== 10

If you do not wish to have your function bind or provide a definitional return use
<transparent>:

>> bar: func [<transparent> y] [return y 304]
== make function! [[y][return y 304]]

>> bar 1020
** User error: {RETURN called--but no function generator providing it in use}

...of course, the console does NOT tell the whole story. The code may not either
but there are a lot of comments. Blog posts and videos forthcoming.

Happy Halloween 2015... and Ren/C'ing is Ren/beliving...

(Note: With the machinery in place, efficiency passes have already begun....)

[hostilefork]

And how are we doing on performance, you ask?

RebolSource:
    >> delta-time [do %make-hostilefork.reb]
    == 0:00:09.31108

Ren/C:
    >> delta-time [do %make-hostilefork.reb]
    == 0:00:10.010641

Doesn't seem too bad a price to pay, eh? And there's plenty of headroom for optimizations with the correctnesses in place...