I have two experience to share:
one at HW, my reserved ticket was from LDH to Doiwala, and had to deboard at DDN in 14632, so I booked the UTS ticket at HW as halt time was usually long and I was able to book HW-DDN UR ticket,
and...
more... second being last week only at Moga Station and that too inside 14630 train from Moga to LDH...
With my experience, I was able to book even from inside of trains stranded on PFs... So i guess you should be able to...