Transfer call directly to voicemail with BLF button

I am trying to give someone the ability to forward a call directly to someone's voicemail and bypass the ringing of the phone. My basic plan is to have a button called Xfer Vmail that could be pressed before someone's BLF button to accomplish this task.

I have configured the following button which does not work.

topsoftkey4 type:speeddial
topsoftkey4 label:Xfer Vmail
topsoftkey4 value:"##*+"

If I push this button followed by the the person's BLF button it performs a normal transfer and the extension rings and rings.

If I push this button then manually dial the person's extension it works as expected and the call transfers directly to voicemail. I am trying to avoid having to manually key in the extension since I already have BLF keys configured for all of my extensions.

Does anyone know if this can be done and if so, how I need to ctreate my button?

Thanks