Set up a menu node mailbox with the desired number, set up mailboxes for the menu options, then re-route calls to the DN that matches the menu node mailbox number in the PBX to the voice mail hunt group.
For example, if your second number is 1500: create a Menu Node mailbox 1500, set up your mailboxes for the menu options, then in the 3300 create a Hunt Group 1500, and Always ReRoute it to the voice mail hunt group.