The FAQ makes reference to donating EC miles, but I can't find a way to do this.

I've got 61,XXX miles in my HH account, with about 20k in the second one. The 20k miles are about to hit the 3 year expiry period.

I'm looking for a way to trigger activity in that account and thought that donating 1k might be a good way to do that as those are essentially orphaned.

Any advice would be appreciated.