First off, this isn't a 'set your hearth to BB' exploit. This is an actual exploit.
Second off, it does require a GM. But I've tested it and it's completely foolproof.
You have to plan this a week in advance to the week you want to win. Here's what you do:
1. Fish up 38 Tastyfish during the contest
2. Split them into 2 stacks of 19
3. Delete them
4. Ticket a GM, say you accidentally deleted them and wanted to turn them in for gold
5. DO NOT retrieve them yet
6. The next week, fish up 2 tastyfish, and seperate them into 2 stacks of 1.
7. Take the 2 stacks out of the mailbox, they will merge with your current stacks (if you did not do step 6 they will simply disappear from the duration timer.).
8. Hand them in.