Unless i'm missing something you cant.  On android you only seem to be able to link your game to Facebook or Google+.  On desktop*, you dont seem to be able to do this and have to create a Plarium account.

* I say desktop, because it seems pretty unlikely you can actually play on a laptop because it seems resolution seems to be the cause of the game not working on laptops from what I've experienced.  For a game that begs for my money as much as this does, it beggers belief that its so poorly programmed in that respect.  Its surely throwing potential users away by being so unfriendly.

Facebook app for Vikings works fine even on laptops.

You can have one account for mobile and Facebook browser version. Not for plarium.com.