1. You buy lots of coins (no matter the name) at the actual price.
2. You create the "bank" as described in the thread.
3. You sell the coins a little higher, the people will buy anyway because it's no risk for them, they always can sell at the same price anyway.
Now the two cases:
a. Price increase: people will cash out the coins to seel them on the market and the bank remain with the profit.
b. Price decrease: people will sell back to the bank, and the banck charges fees and remain with the profit.
Once again great business ideea, but no really benefit for the coin.
Oh, not incompatible with what I said, but it is a one-time business then.
After the capital has been sold, you cannot continue your operation.
And if you expect to buy back the coin (probably at higher price) and start again ... well ... this would become a bigger and bigger bubble. It would surely pop at some point ^^