This is very hard and I have a fourteen yr old tortie just like this.
I have a cage carrier, quite large and one end opens completely.
I am afraid that I have to trap her and it starts by closing all the floors and blocking up the stairs.......usually fail on the latter but basically I have to get her trapped in a corner by the cage with door open. She will cry pityfully and it breaks my heart and she will freeze.
I cover the cage completely on the closed sides and top with a towel and once she is trapped I talk to her quietly and stroke her..........when I last did this she would not let me touch her..................and try to push her gently in and shut the cage door.
It can take for ever and have an agreement with vets that as she is semi feral I catch her and then ring and say we are on the way.
Maybe if you havent got a cage type carrier, you can improvise with a large cardboard box from which you can then make a hole into a normal carrier from which he can walk through.............once in the carrier tip it up so he cant get out to shut the door. I would also put a towel over the carrier and keep it covered for the journey.
After running away about Jul last year and staying out until jan/feb, except for rushing thro the flap to eat and straight back out, Sasa has been living totally indoors and after her being here for 7 years she now wants to be stroked
She is very heavy and strong.