You can go ahead right now and book this ticket for travel to Europe in August at the off-peak rate, if you book it as a one way ticket with a stopover at a US gateway city, and fly to the stopover city during the off-peak season.

For example - LGA-ORD on May 1, and ORD-LHR on August 3. Cost varies depending on where you live. I don't necessarily think this gaming of the system to allow international legs to be flown in peak season for off-peak miles should be allowed, but it currently is.