I've never used E6000 so I can't help there unfortunately. But I made my niece flip-flops with shoe goo, clipped it and let them dry for 24 hours, same as you did with E-6000, she wore them last night and didn't have a single problem.
I know that doesn't help for the shoes you have already sold.
You can get the shoe goo at Wal-Mart, among other places. At Wal-Mart it's $4.