Ex-prisoner John Crilly, 48, was a close friend of one of Khan's two victims, Jack Merritt, 25, who helped to rehabilitate him.
He sprang into action alongside a chef armed with a long pole to subdue Khan, who was wearing a fake suicide vest, on London Bridge before police shot dead the terrorist at close range on 28 November.
The pair were course co-ordinators on the Learning Together programme, which is aimed at bringing offenders and people in higher education together to "study alongside each other".
Crilly served 13 years in prison after being convicted of murdering 71-year-old Augustine Maduemezia when he and his associate David Flynn broke into his Manchester flat.
The pensioner died from a blow struck by Flynn.
Crilly's conviction was quashed after a Supreme Court ruling which said the joint enterprise law - where defendants were prosecuted for murder even if they did not strike the fatal blow - had been misinterpreted.
He went on to plead guilty to manslaughter and was released on licence last year.
It states: "John has a part-time job, but can barely support himself financially. The few clothes he had were left at Fishmongers Hall on that terrible day so he literally only has what he was wearing as he bravely fought a terrorist. This man showed great courage and until the media revealed his identity he would have continued his life as an unknown hero.
"We want to raise money for John so that he can start to rebuild his life with some level of comfort. He would like to have the simple things that most of us take for granted.
"He dreams of having his own car so he can maintain contact with his children who live hundreds of miles away, but right now he can't even afford driving lessons. He wants to spend Christmas with the people he loves, but he shares his accommodation with nine other men so can't have visitors stay over."
Jengba says Crilly, who graduated with a law degree in October last year, wants to continue studying and working alongside the Learning Together team in Cambridge.
The campaign group went on: "We believe he will be a wonderful asset for this amazing initiative. We all know that Jack Merritt was a very positive influence on John's life and all of us at Jengba have seen the devastating impact both his and Saskia deaths have had on him.
"We want him to have some financial security so that he can continue the work that Jack and Saskia were so passionate about. So he can help others in the way they helped him. So if you can help John do that, however great or small, it will be hugely appreciated."