Carpets are usually help down by grippers, put a screwdriver (a clean one, not the one that you've just stirred the paint with) under a corner or edge, once you've got an edged up it should be fairly easy to remove the whole carpet. Then hide it behind the shed and deny any knowledge of having a carpet or rush down to carpets 'r' us and demand an emergency replacement.
A higher risk strategy would be to use some white spirit (assuming that's what you use to clean the brushes with) - test on a small portion first. Dab on the the stain and blot away with kitchen roll
Good luck!