How to pay for a transaction from one account with the ether balance of another account?

Hi,
I was wondering if there is any way to create a transaction signed by one account, but using the ether from another account? (assuming both accounts are managed by the same node).
For example, I am calling:

myContract.myFunction.sendTransaction(param1, param2, {from: address1, gas : myGas});

Is there a simple way to pay for gas from an account other than address1, that I also control? For example, my coinbase?
Any help would be greatly appreciated, even if it's just explaining that it can't be done!
Thanks!