Adapting Custom Actions for 32/64-bit OS

Hi,
Using WISE, I have created a MSI for Windows 7 32bits.I have custom actions that are calling binaries (complied to support 32bits). What is the best practice to manage the custom actions in my current MSI to support 64-bits also (assuming compliing the binary files to support 64-bit). is there a condition for 64-bit or 32-bit I can use for each CA, or is there a better way....

Thanks.