Setting Custom RPC URL for eth_sendTransaction with createTransaction() API

I’m currently using the Fireblocks Web3 provider with ethers and I need guidance on how to set my own RPC URL when using the eth_sendTransaction method, specifically with the .createTransaction() API call.

I have subscribed to a Sandbox account, but I’m having trouble finding the right way to configure this. I noticed the recently added nodeControls feature in the documentation, but it’s unclear whether this is the solution I need, or how to implement it effectively.

Any insights or examples would be greatly appreciated. Thank you!