[brunie's mom]

Found this on 'marvistavet':
The Uncomplicated Hygroma

The simple hygroma is not painful and is mostly of cosmetic concern. Changing the dog’s bedding generally solves the problem though sometimes special pads or bandages for the elbows must be constructed. If the dog begins to lie on softer more pliant materials, the hygroma is likely to simply resolve over 2-3 weeks. It is best not to tap off the fluid as any time the hygroma is pierced, infection can be introduced, creating a “complicated” hygroma.

Looks like sleeping on soft things will help. You could also try to construct an elbow pad...maybe something you could find at Shoppers Drug Mart that would cover his elbow such as a wrist pad...and put it on his elbow?

Once the weather cools down...he should be more inclined to lay down on something soft.