No, as far As I know, you cannot.
LRC is the ITU standard.
LCR is the film order, but it's just a convention, not a real standard.
Steinberg choose an international standard, and it's better that way IMHO. But anyway it's not really important :
When exporting an interleaved 5.1 you have 3 possibilities :
1. It's a stem or a specific sound that needs to be re inserted later in Nuendo : you can leave it in the LRC order, interleaved.
2. It's a deliverable : you have to go for separated mono files.
Everyone ask for six mono files because you have in fact some other different orders possible, for instance LRLsRsCLfe, or LLsCRRsLfe and so on.
And a lot of software use a lot of different channel order. Not one is capable or reversing it's native order for exchange reasons...
With mono files, everyone is happy !
And yet again, .L .R etc is the protools naming convention (you get some others as well) and in Nuendo let you choose that.
3. You have to deliver for a specific theater or for special diffusion directly, or sometimes some DCP authorer, and they ask for wave extensible (a glimpse in the future...)
This format allow additional metadata to BWF files to specify which stream goes to which channel. (No need to go for mono channels, then)
It is really cool but remains for specific occasions only... Because lots of others (old) daws don't understand that format.
Anyway, mono files is the main way to go for 5.1.
I even use that for sound banks.
Hope it helps