Surround Mixing / Stereo monitoring with Soundcode Stereo

[Meads]

I know this sounds rather unprofessional, but here is my situation:

A customer asked, if I can do a dubbing mix of a 5.1 feature. I only have a stereo setup monitor-wise, but I can handle 5.1 in PT.
Since dubbing is only about dialogue I don't really need the 5.1 feel for mixing. So could I use Neyrinck Soundcode Stereo on the Master Aux to get a stereo downmix, which I listen to, while I am mixing, but delivering the 5.1 mix?
I mean, does it make sense, or will my mixing be hokum, based on just listening to the simulated downmix?
The customer knows about the issue, but he gave me a go, if I can manage it somehow.

Any input appreciated!