Mr Milroy said maintaining a positive mindset was crucial.
"Mentally, I have been telling myself I am able to climb it. Believing in yourself is the most important thing."
He has also been receiving help from Carabiner, a mentoring programme for youth with disabilities and an initiative of the YES Disability Resource Centre.
"It works by setting goals," Mr Milroy said. "Mine was to do with sports and they match me up with somebody in the sports industry. We work on this goal together."
Carabiner co-ordinator Cam Calkoen said he was inspired by Mr Milroy's "desire to make a difference".
"His passion and vision are second to none, but what I really admire is how he's looked at the bigger picture and said, 'How can I use this to create awareness about disability?"'
Mr Milroy has also been fundraising to buy off-road wheelchairs for disabled youth in Samoa. He said it was a project that was close to home.
"Growing up in Samoa and having a disability means access is a big barrier in normal everyday life. Knowing first-hand about this, I wanted to give something back."
With just over a week to go, Mr Milroy said that despite feeling "a little bit scared", he was looking forward to the big day.
"There's a fire burning inside me which can't wait to climb this baby."