I'm sure people who actually know what they're talking about will chime in soon enough, but...
I would assume you bend a suitable gauge piece of steel to the right shape, then slide the catheter over it, and gently heat it with a heat gun or hair dryer, until it softens and takes the shape.
And umm stitch it? Then tie it off several times. Maybe even run two lines, with a little extra slack on the second, if you're paranoid and want redundancy.
Just make sure to sterilise the fuck out of everything.