All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is not permissible for your friend to perform the obligatory prayer while sitting on a chair because standing while performing an obligatory prayer is one of the pillars of the prayer and one is not exempted from standing unless he is not able to stand.
What you mentioned about his job and the small place where he works is not a sound reason for not standing. Rather, he can perform the prayer at any close place where he can stand as the entire earth has been made a place of prayer.
However, some Muslims who live in non-Muslim countries – may Allaah guide them – are careless in performing the prayer and in observing its pillars because of being ashamed to be seen praying. This is indeed a dispraised shyness and a feeling of inferiority whereas they should be proud of their religion, as all honor belongs to Allaah, to His Messenger, sallallaahu ‘alayhi wa sallam, and to the believers.
Indeed, many Muslims feel proud of the rites of their religion and perform the prayer in non-Muslim countries in their work place, and this was a reason for many non-Muslims to be guided to Islam. For more benefit, please refer to Fatwa 81837.
Allaah Knows best.