Technically...

An FO who is fully typed in the aircraft can log sole manipulator PIC. I also cannot find any legal reason why someone with only an SIC type could not do the same although that seems much more open to interpretation.

But in the US this time would be useless for airline hiring purposes, and if you did not make a clear distinction between your sole-man PIC and your real PIC an employer would assume that you were trying to misrepresent yourself..buh-bye!

Yes, it's legal but if you want to do it you had probably better log it in a separate column.