How to reduce from SATB to Unisono

Hi friends and musicians,
at the beginning of a new score it is usually to define the instruments or voices, like soprano, alto, tenor and bass. This will be gilty for the whole score. But in my case one part is written for 4 voices, the other part should be unisono (all voices sing soprano). How can I realise it, that the unisono part is written with the only requested line? For example by making invisible 3 of 4 voices (A, T, B) - but how can I do it?
Thank you for your kindly support!
Toni