There have been one or two ideas coming out of string theory that give similar possibilities, stuff like adjusting the size of dimensions in order to change the properties of space. All but one share the same problem, of having to propogate an effect ahead of you at faster than lightspeed locally.

The exception was an idea coming out of the concept that there might be something acting a bit like an extra extended space dimension that was only accessable to gravity. If that were true you could curl the bubble that the ship was in around in this extra dimension and partially ahead of itself, using conventional mass outside of the space being affected to give the effect of repulsive gravity. I don't think anybody takes that hypothesis seriously anymore though.

Of course, the problem with nitrogen is that nitrogen = finer bubbles in the head = waiting longer to drink your beer. Actually, I was in a pub in Ireland once, and an (American, strike 1) girl ordered a half-pint of Guinness (which is strike 2 against her in the barkeep's mind; a half pint?). When he finished pouring it, he set it on the counter, and she immediately reached for it (strike 3). He smacked her hand, and told her to sit down and wait. She had no idea what was going on.

She later tried to order a "Smith Wicks" and was told, "never heard of it"...