Is the freelance gig seasonal? Maybe do the Europe trip during the freelance gig's off-peak period?

I personally find most cities in Europe much better in March-May or Sept-Nov. If you're going south, then add most of the winter months outside of the peak Christmas period as well.

Then you'd almost certainly find your J seats, and wouldn't need a huge lead time to get them. Maybe 3-4 months...

(That said, June isn't bad...it's better than July-August. Not that this is stopping us from going to Vienna and Barcelona next month...it's just that I like it *better* when the tourists aren't there in droves.)