If it's within the same brokerage just ask for a block account(?) that way you will get the same thing in both accounts. Let me know if you are under a different arrangement and will try to be a bit more creative.
If master account use limit orders and I will copy limit orders, order can be executed on my account only according to price difference. I think it is only one way to copy - wait before order will be executed on master and then send market order to my acc.
I assume you are managing multiple accounts. On our software, you can create an order ticket with one account number, send, then change account numbers and hit send. If this being done as a CTA or RIA or if you prefer to execute once then allocate, we offer that on Real Tick and Sterling Trader Pro for equities and all futures though block trades like Matt said.
The master account is your account. It includes your account and/or any POA you may have. It's just all aggregated in one one account. This is what people do when they trade their personal account, IRA account and wive's cousin who bothers you daily to trade for him(example). There is no need to send market orders if you place limits. When you set up the block account you need to also disclose your allocation in case you are trading as a POA for someone.
Our software has a copy trade feature. You place a limit order in one account and it places the same limit order in other accounts. If you modify your original order, it modifies all the limit orders it placed. If your limit order gets filled but the copied orders do not get filled within a specified time, they get converted to market orders.