change the floor. it's cheap and easy DIY. specially with laminate.
when i was living in the place with carpet-i did exactly what Scataphagos proposed. well.. maybe a bit different..you buy a mat at local staples(made by\for staple)-use it. when it's crack-buy another one and return old one using fresh receipt from staples
Maybe consider a quality medium pile persian rug that'll help tie the room together. Cut up old plastic protective mat so it's a bit smaller than persian rug footprint, thus completely hidden, but more supportive for casters. You never know, http://www.youtube.com/watch?v=ezQLP1dj_t8
If you have very high grade carpet, shouldn't need a plastic/glass cover. I did this for years before ripping it out and putting in Walnut. Casters never left permanent mark/divot in carpet.