Creating Sub-Auto Numbers

Hello,

We are currently using a web form for customers to submit a service request. After the form has been submitted a auto-numbering confirmation is generated and the customer is sent a notification with that confirmation number. When we process the request we often need to split the service request into multiple services with each service requiring multiple drivers for each service. Is there a way to create a sub auto numbering (Children) if we need to split the request into multiple services and different line items for the different drivers? 

I.E. (AUTO NUMBER) Con# CD_02111

(SUB-AUTO NUMBER)                    CD_02111-a

(SUB-AUTO NUMBER)                     CD_02111-b

(SUB-AUTO NUMBER)                     CD_02111-c

(SUB-SUB-AUTO NUMBER)                          CD_02111-c-1

(SUB-SUB-AUTO NUMBER)                           CD_02111-c-2