Think of the physical reason for why we off-gas internally. There is a solid mass of waste matter sliding along an intestine on it's way to the exit. As it slides along it compresses the methane[between it and the exit] that is being produced by decomposition of the waste matter. When that gas gets so compressed at the exit point that it overcomes the resistence of the "exit portal" that portal relaxes and allows the gas to escape and you better be near a john because you know what is coming out next.
Now the reason I say that it is physically impossible is because it is my understanding that flesh and liquids inside our body are not affected by increases in pressure but the gaseous voids in out body are --lungs, sinuses, tooth cavities, BOWELS, inner ear, etc. If a freediver goes down to 200' the ambient air he took in on the surface is compressed in the lungs to almost nothing in volume. If YOU have ambient air in your bowels when you go to depth, that air will also be greatly decreased in volume which means it will not be putting pressure on the "exit portal" to cause such portal to loosen up thus off-gassing. The downside is that the waste matter will no longer have that gas between it and the exit so you better be wearing DEPENDS!