I see that while I was fizzing around trying to compose an answer, Rudestuff stepped in to comment. But I'll post what I had written as it gives some documentation to the answer.
Crusherrr,
I'm going to play jailhouse lawyer here and say you
can user your time as "sole manipulator" of the controls as an F/O toward the PIC requirements for an FAA ATPL.
Here are a few FAA letters of interpretation addressing this issue. You'll find it addressed in part of each of these letters:
https://www.faa.gov/media/15551
https://www.faa.gov/media/14521
https://www.faa.gov/media/11911
I had a better one which I now can't find. But the gist of it was that the FAA realized a long time ago that for a person entering a Part 121 operation as a person with minimal PIC time, it was hard to get the required PIC time for an ATPL so they allowed "sole manipulator" time or PICUS to count for purposes of getting an ATPL.
Don't bet the grocery money on my version of this. Rudestuff or B2N2 will come along and concur or set the question right.
In any even, good luck.