Ben Vale, 36, from Claverley, is being joined by his friend Andy Tamplin, in spending a day sitting in every one of the 9,875 seats at the Montgomery Waters Meadow Stadium, the home of Shrewsbury Town Football Club.
The pair will be taking on the challenge on July 1 and have been inspired by the plight facing Ben's nephew, 19-month-old Gunner Lewis-Vale.
The youngster, from Highley, was diagnosed with a rare mucopolysaccharide disease, MPS Type 1 Hurler, which means his body cannot convert sugar into necessary protein in the body.
Gunner’s doctors have said his best chance of survival is with a stem cell transplant before his second birthday later this year.
His family have been raising urgent funds to add more donors to a stem cell register – it costs £40 to recruit each potential donor to the register.
Last month they hit their £10,000 target, while Ben and Andy's fundraiser has already surpassed its £2,000 target, reaching £2,605 on Tuesday morning.
Ben said they had wanted to do what they could to help – be that with raising awareness, or potentially funds to help towards future care for Gunner.
He said it had been heart-breaking and a huge shock to see the youngster diagnosed with the illness.
He said: "Initially it was a real shock to the system. Really upsetting. Once you understand the situation a little more, because I had not even heard of it, I didn't know it existed, you are learning about what is to come.
"There are going to be a lot of changes in Gunner's life that will affect him and the family. We are just trying to think of ways to support them and to plan for tomorrow.
"The basic thing is to push the stem cell donor register and encourage people to join but also to think about tomorrow and what will be needed – adaptations to the house and support for Gunner as the disorder takes a toll on his body."
Ben, a father of two himself, said the reaction from the local community to Gunner's situation had been overwhelming.
He said: "The support have been very humbling and a real testament, it is what you get with a small community and the kind-hearted nature of Salopians.
"It is amazing and just absolutely humbling to see people donating, it has been going up hourly and the notifications keep popping in. Thank you to everyone."
Ben said the actual challenge could well be harder than both he and Andy expect – and said they have been practising in the stand at AFC Bridgnorth, and have also been to see the task ahead at the Montgomery Waters Meadow.
He said: "We have been spending a couple of hours in the stand. The biggest challenge as much as physically will be the monotony. 9,800 times sitting down and standing up. I am also just shy of six feet and have abnormally long legs so I kept cracking my shins on the seats in front."
He added: "Thank you to Shrewsbury Town, they have been brilliant, really excellent and so supportive of the cause since the get-go."
People who wish to donate to the cause can do so at justgiving.com/crowdfunding/bumsonseats?utm_term=ZmZYBmzMn.