There's probably an easier way, but just enter a trade and the £50k will magically appear. If you don't want to make a trade yet, just buy 1 share in something and you will appear on the leaderboard. I have justed shorted 1 Sainsbury share to open my account.
My money magically arrived with no shorting needed, I can't say I like to guess what even one sainsbury share will be worth at 9.00 am although I am quite likely to know by 8.15
Peg
ps. damn that last ANL trade, if I had stayed out like you did, I would have pipped you