Modifying Cory Fowler's CAN bus MCP2515 library for use at slow data rates

I seem to be having some issues with the transmit function as well. So I created A receive and Transmit FIFO in my program. However, I am looking for a way to determine that a transmit buffer is available before sending a message just so i can do other things in my code without having to wait for a buffer to become available.
Any one know how I can do this?