Would partner flights (i.e., US) help with the 500-mile minimum? I seem to recall Elite Maximizer wanting to sell me <500 miles when I was booked on US LGA-DCA. I was connecting to CO in DCA, so I had my OP number in hence why it offered the maximizer.

This would be very roundabout, but might work? Looks like US flights are easiest booked through United.com, so you'd probably have to book a short US (UA codeshare?) flight on United.com, put in your OP number, buy the miles, then cancel via United.com. Might be worth a shot, at least, since e.g., LGA-BOS is only 185 miles and if this works it would be much cheaper than 500.

On second look, I got 500 EQM and 1000 RDM (500+500 bonus for being Plat) for the US LGA-DCA flight, so maybe this trick won't work. Sounds like it wouldn't be any worse than picking a CO flight, though.