How to butt into cove cornice?

[MGusto]

Hi there

I have had a pantry installed in my kitchen and as you can see from the photo, the job requires 90mm cove cornice installed around the bulkhead.

I do not want to cut into the existing cornice, but but into it with what I think is called  a scribe joint. I watched a video on how to cut  a scribe but I just cant picture how this works with a cornice.

Can anybody out there help me out.

I got a quote from a gyprocker who normally charges $450 minimum but he would do the job for $350 without painting.

For a $10 piece of cornice I am gonna do this myself!

Cheers

Mike

PS

I have a needle file(?) that can take the shape of the cornice. Will this help?

[Nailbag]

Nice work @MGusto