Prefix and then the rest manual number?

Is there a way to have a prefix for Document type number and then after the prefix, the user can manually enter their own number?

Right now it's auto-generated with the prefix, ECOForm-1xxxxxx.  The user then renames the number but leaves the prefix (the number ends up being the same number as the drawing number). 

OIR

<AttrValue

     id="number"

     algorithm="com.ptc.windchill.enterprise.revisionControlled.server.impl.NumberGenerator"

     ignore="false"

     force="false"

     final="false">

     <Arg>ECOForm-1</Arg>

     <Arg>{GEN:wt.enterprise.SequenceGenerator:WTDOCUMENTID_seq:6:0}</Arg>

   </AttrValue>

I'm wondering if we can have the number generate the prefix, but allow the user to enter the number while creating the document record.  Is that even possible?  Or can the system find the drawing number and generate the ECOForm number to match the drawing number? 

For example if the drawing number is 96-14-012, then the ECOForm-96-14-012.

Does that make sense?