"Splitting" staff

Hello,

I'm transcribing ancient music at now. So, we know that that kind of music uses differents clefs for it's voices, specially the middle ones.

So, i need a manner to put the original clefs in my score, to help the voices' choosing, and to create an ambitus [ambitus is the whole vocal extension used by a voice], because, some voices on Palestrina's works, don't match with it's description [e. g.; In the attach, the "tenor is a second alto], but the 'real' score staff, where i'll write music, must use the modern clefs [alto must be on g-clef, instead of 3rd-line-c-clef]

So, how can I do this? If not, this feature can be included on the next release?

PS: The fragment is from:

Pater noster - Palestrina's Opera omnia, Tomus tertius, Breitkopf und Härtel; 19th century.
Taken from imslp.org.

Thanks.