A more realistic way of creating a random stock price pattern might be to imagine an x sided die, say one with 21 sides, and then throw it 10000 times. The facets of the die would be numbered +1 to +10 and -1 to -10 and zero (to represent unchanged).
Then start your chart with an arbitrary stock price, say 100, and start throwing, adding each result to the running total. So you might get 100, 101, 100, 103, 102, 99, 99, 101, 102,104, 107, 105, 115, 111 etc. Then plot this on your chart as just closes. After a while it may start to look like a typical daily stock chart. I don't know how to incorporate the OHL bit though!
However stock prices do not generally move up or down by 10 as often as they move up or down by a lower number, so you might want to load the die so that the higher the number, the progressively less chance there is of it coming up. I don't know whether, for realism, this progression of chance should be logarithmic or linear. Try both perhaps. Either way the outcome then won't be truly random because it is weighted towards the lower numbers, more like a stock price movement.
Anyone fancy trying this on a spreadsheet?