In sx 2000 this can be done . In 200 I don't know but maybe is posible too :First do what DrPbx says than open the ARS form and type at leading digits 3 (not 3457 ) and you'll see the 457 in the first line . Complete the form with the others line with digits to follow needed (like 567 for instance ) with the others fields like the fields in the first line (0 at number of digits to follow and the same route number and type).
The only limitation is at digit blocks not at route numbers ,( because is the same route). In form "Dimension And Feature Display" (in the Sistem Forms) you'll see the max available digits block and number of digit blocks used- you should check this one from time to time at ading ARS.