Advice on developing a stock simulation game

Hello, I am trying to develop something similar to HSX. It is a prediction market
that attempts to predict box office. The specific part I am trying to model, is the
fact that the trades can buy/sell against a virtual market maker. So those orders are
filled immediately. In fact, the vast majority of trading is done against the virtual
market maker immediately.

Then the imbalance between buy and sell orders are entered into a formula to determine
the market price.

"https://patents.google.com/patent/US7487123B1/en"

"The projected price movement (PM) can be expressed as: PM=(NMS/LMV)*SIV."

"For example, with 42,000 buy orders and 30,000 sell orders for a particular stock,
the NMS=(42,000−30,000)=12,000. With SIV=$0.25 and LMV=5000, the price movement of
the particular stock will be (12,000/5,000)*0.25=$0.50. Thus, the market price of
the particular stock will be $0.50 greater than the last trading price."

I read through the patent a few times, and could not figure out how SIV is determined,
so I cannot adopt the same formula.
But is it possible to adopt the same strategy? To have the trading done against a
virtual market maker and filled immediately, without having to match up buys and sells.
And determine the price through some other method?