choral voice part splitting

[Chris Caudle]

I am just learning Lilypond, and am having trouble understanding how to notate 
a style which is common in choral music.
I am entering a composition for SATB voices, so I am creating a sopranoMusic, 
altoMusic, tenorMusic, and bassMusic section, and will use partcombine to 
place the two female parts in the treble staff, etc.

My current problem is that occasionally one of the voice parts will split, 
e.g. the soprano part will split to independent soprano 1 and soprano 2 
parts, but only for a few note, then back to a single soprano line.
Since the parts split so infrequently, it does not seem the best approach to 
enter the notes as if it were an eight voice composition.

When the split parts maintain the same rhythm, I am able to enter chord 
notation in a single voice (e.g. <c e>1 ) and that works OK, but when the 
rhythms are not identical, I do not understand how to enter the sub-parts 
within the same voice part.  I tried to use chord notation so that the notes 
were stacked, but with different rhythms, e.g. <c1 e2> d2 but that was 
flagged as a syntax error.
So what would be the proper way to enter that example, where the sopranos 
split, with part of the singers for that voice part sustaining a whole note, 
while part of the voices sang on a half not rhythm?

thanks for any help, 
Chris Caudle