Add a "smelter" to the BOS. The smelter would allow you to "melt" resources (keys and souls) into gold... This would bypass the need to open souls an then go sacrifice or sell the characters. it would also allow users to essentially sell keys, which is currently not possible.
There could be a cost for smelting, so as to not allow unlimited profiting. Smelting cost could be the same as the converting souls to characters cost. And gold returns would be the same as if the characters were sold. It really would just bypass the whole covert to character, then go sell the character in the My Team screen. Really jsut more of a "quality of life" alteration where souls/characters are concerned... with the addition of the ability to get gold returns from excess keys.
If items are dropped into the smelter, a pop up could appear similar to the sacrifice popup...
Then there would be the standard reward popups showing the amount of gold earned from smelting.
Just an idea.....