Change the value of a note without changing the its notehead shape

Hi,
I'm working on a project which targets the notation of a simple liturgical recitativ but in four voices. For economical reasons, two voices are collated into one staff.
At some points, where the pitch is the same for several syllables, the shape of the breve is used instead of dozens of eighths (quavers) for the sake of better readability. In this practice the value of the breve does not defined strictly, the same notehead can represent any number of eighths, depending on the number of syllables. This practice can be followed seamlessly until the number of the syllables are the same in the system.
Now, I'd like to recreate the notation, presented on the attached image. As you can see, the first breves in 2nd, 3rd and 4th voice must represent five eighths, because of the five-syllable long tune in 1st voice.
My question is: how can I modify the value of a breve - similarly to the difference in nominal and actual timing of a measure - to lasts exactly for five eighths duration (it this case) and keep its notehead shape?

(There is no problem with the second group of breves, because although they represents five eighths also, those sounds in perfect unison in each voices.)