Trains from North like UMB, CDG and travelling towards JP, AII and ADI can take this detour to avoid travelling thro crowded Delhi region. Potential contenders could be CDG-BDTS SF express, and some specials also.
The rout would be PNP-ROK-Rewari-Narnaul-Nim ka Thana-Ajmer or Rewari-Alwar-Jaipur- Ajmer and onwards to Ahmedabad.