Is it possible to work in EG (Extended Gamut, cmykogv) color mode in Photoshop?

Both, Photoshop and Illustrator allow to work ECG; On Photoshop trough Channels; On Ai y have templates with OGV swatches and when I need them to interact with CMYK objects, I simply tailor appeareances mising whatever I need.

Photoshop functionality like Layers only works in grayscale, RGB, Lab and CMYK so far. 

Has your print provider provided you with an ICC Profile for their specific CMYKOGV-process? 

Better to work in RGB and convert at the end,

The very well respected GMGcolor have a plug in for EG that’s worth exploring. 

user thoughts on the GMG product

I hope this helps
neil barstow, colourmanagement net :: adobe forum volunteer:: co-author: 'getting colour right'
google me "neil barstow colourmanagement" for lots of free articles on colour management

Hello, do you really want to work with a reduced set of tools? 

I would rather recommend to work in RGB, and preview the work with your chosen color mode using View / Proof colors (after setup in View/Proof Setup)

You can convert to an installed multi-channel profile using Convert to Profile and pressing the advanced button.

The result will be a multichannel mode file embedded with the conversion profile.

The preview may or may not be accurate.