Hi Jasmine, no you cannot use your 40D flash as master. Wireless remote is for taking photo only, not for triggering flash. You can use STE2 for triggering flash or set 580EX, 580EX Mk II or 550EX as master to trigger slave flash, such as 420EX ... Some 3rd party lens are pretty good too, like Tamron 90mm for macro 
Warmest Regards
Desmond
Warmest Regards
Desmond