u need to approach cstm prs i guess. you will be redirected to reservation superviser. give an application in writing about your itinerary and scheduled stoppages. you will be called after two days. the application may be approved with a window provided for you to complete the itinerary or necessary changes required will be suggested. jus few points-
1 origin and destination should be same
2 no route can be repeated unless absolutelly unavoidable
3...
more...

no premier trains like raj/shat/dur/garib rath/yuva, etc
4 if you miss one leg, remaining legs become invalid
5 fare will be twice the fare of half the distance
6 you can opt for same/lower class through out
7 all fare needs to be paid while collecting challan
8 carry the challan to any prs and book the tkts
9 window period begins from the departure date of ur first train
10 maxm 8 break points and minimum 4 allowed
11 challan can be applied for more than 2 months in advance
12 it can be availed for any class...sl/3a/2a/1a/fc/cc/2s...