Signal routing solution

[Mark Hamburg <mark_hamburg@baymoon.com>]

(Insert comment from Mark Sottilaro about how the EDP needs to be 
stereo.)

I'm reworking my minimalist rack. (Now that everyone is going to DD-20s 
and the like I no longer feel quite so minimalist, but so it goes.) I'm 
faced again with the problem that in what would otherwise be a stereo 
signal flow, I've got a mono EDP. I'd be fine running the EDP in the 
center channel if I had a way to preserve the stereo signal passing 
through the EDP. I've dealt with this in the past with a line mixer, 
but the Passac mixer is both noisy and consumes one rack space that I 
might be able to put to better use. Can anyone suggest something that I 
could stick in the back of my rack to sum the left and right channels 
to mono and mix them with the mono out from the EDP? Essentially 
something that accomplishes the following

        L ----|----------------+------ L
                   |                      |
                 + ---EDP ----{
                   |                     |
        R----|----------------+------ R

Thanks.
Mark