What effect would this have on the market if the buys and sells were almost back to back?
Almost none. 290 btc is about 1/500th of MtGox's weekly trade volume assuming very low average days of 20,000btc per day. Today alone there was over 100k of traded money.
You can quite smoothly buy that amount of btc, transfer it to employee, and then he/she sells it back. The market will neither care nor notice that amount of funds.