Well, I guess this one's for DancingDoc to point out, but for my part I'd say don't force it whatever you do.
My instructor has comparatively poor turnout, and I'm grateful for that - it reminds everyone that good turnout isn't actually essential for dance. I think it's not so much about achieving +/-90 degree static rotation of the hips, as learning to start using the muscles that would give you 180 degree turnout if you had the flexibility.
The only "exercise" I do for turnout is when I'm warm & lying in bed: lie on your back, bend your knees, & gently let your legs roll out either way as far as they'll go of their own accord. If you relax totally you should feel you knees gradually sinking - as far as I know, this gently stretches the muscles (& eventually tendons, I suppose) without risking straining anything.
For staying flexible in the office - I have a good excuse to bend down & fetch something that's almost at floor level every so often, so I surrepticiously practise my plies! Stuff stacked on high shelves is great for releves, and reaching over for something allows the odd arabesque. Tendus & ronds-de-jambes I practise, when no-one's looking, while I'm standing at my workbench. Anything more energetic is distinctly dangerous (I work in a laboratory with lots of apparatus & glassware around me), but I have been known to break out in to waltzes when I've got a CD on....
Actually, as a footnote to the comment about plies - they come in very handy in the workshop: easily the safest way to lift a 30 kilo indexing jig off the floor and on to a milling machine!
A.[/i]