The 48-year-old former Carpenters Arms star has been registered in time for Saturday's trip to FC United of Manchester.
Special dispensation has been granted by the National League to complete the post-deadline signing following a number of injuries currently affecting the United squad.
League spokeswoman April Fool told bufc.co.uk: "We are happy to help Boston United in this instance and understand Neil could fulfil a lifelong dream by making his Pilgrims’ debut at the weekend."