If laying your car up for a period of more than a couple of weeks, it will be beneficial to over-inflate the tyres by about 10psi, providing this doesn’t exceed the maximum pressure marked on the sidewall. Keep them topped-up and periodically jack and rotate each wheel to ensure it doesn’t sit too long on one spot.
Alternatively, you could elevate the car on axle stands – but this may have a negative effect on suspension bushes, which don’t like to be held outside their normal range of movement for too long. The best solution, though, is to get a set of old wheels and tyres and fit them over the winter. Stack the good wheels and tyres horizontally and keep them out of direct sunlight.