Because you are using a CFlash part you will need an external micro to put the device into programming mode (IAP is not available on this device) and just upload a custom bootrom.
You could adapt my prgrammmer to do this. (www.spen-soft.co.uk) Or if ST would document the 'RAM Exec' function of Visual Programmer you might be able to do it from there, but you would still need a means of uploading the custom bootrom. Regards Spen