If you look under candlesticks and change the view to 1 day you can get historical volume that way. It's not perfect but maybe you could pull the data and average the volume/price over the entire day.

Is there no way you guys could set up a defacto brokerage for trade? You own all the volume anyway; exchanges would have to follow your spreads rather than the other way around. People will always try and make a little by arbitrage but if you offer a way to trade without any slippage nobody will bother using exchanges to buy and sell clam. The market wouldn't exactly be "free" but trying to set a floor on poloniex is no different. At least you'd could control the spreads instead of poloniex