I also did this mod when living in uni halls. A trip to Wilkinsons (aka Wilko) will sort you out. Buy a cheap hacksaw for a quid or so, and a multi pack of tape. Saw off the heavy brass end of the pole. No one needs that much metal in a cherub. Get your UJ, and wrap it in as much tape as is required to be a reasonable fit in the end of the pole. Next, go out for a big curry, with lots of beers, and potentially an early morning kebab.
By the morning, you will almost certainly have a brewed up something catastrophic, and 10 minutes in the john will have resulted in a blocked toilet... go to your halls reception and call in the issue as urgent. "Send a plumber, NOW!" Within a matter of minutes (maybe hours), someone will turn up to sort out the problem... and then you pounce. In their state of shock and horror when witnessing the plumbing delight, you ask if you can borrow their drill. They'll no doubt be delerious due to the injestion of airbourne particles of Kingfisher, Vindaloo, Donner meat and yesterdays lunch by this time, and they will be unable to say no.
Wedge the UJ into the new tiller, drill a hole in one side, and pop in some sort of screw to stop it coming out. Then apply more tape around all of it. Thank the plumber for his time. Perhaps open a window for the poor chap, and leave swiftly.
Congratulate yourself on a job well done. Celebratory beers and curry anyone?
(this is how it was in my day anyway... uni might have changed since)