The airport is, of course, at Stornoway. And it has cars from Sixt, Thrifty, Easycar, Opodo and ebookers (inter alia). So a one way shouldn't be a big problem

I saw that too - but when you plug in SYY there aren't any of those majors listed.

The airport's own website only shows Stornoway Car Hire - and says cars may not be taken off Lewis/Harris.

oops - meant to say " . . . may not be taken off Lewis/Harris except in special circumstances w/ prior written permission"