This achievement blows and I am only four gold coins away from getting but I thought I would test an idea and it did work.
1) When you toss a gold coin in the fountain you get a 2 minute buff which helps you get more coins.
But--
If you are in a party and they are fishing beside you they also get the buff but it does not show on them.
I tested this three times with guild members and people that only had 378 skill were getting coins (two or three plus) while the buff was active on me.
So long story short if you can group with guildies or convince others at the fishing hole to group with you this pain in the ass achievement can be done alot faster.
Finally found something to put up here!! Small but its a start.