Take a look at Plink options for working with haplotypes here.
I have been recently using it quite a lot for some haplotype calculations, and sounds like it might work for what you want, if you specify the haplotypes.
But I don't know if sequences as large as fasta are gonna be accepted. Anyway looking is free, and the plink tutorial is really good! ;)
Do you know if this supports multiple individuals? I don't want it to collapse the individuals into a consensus .
I haven't used it for this, but it does have a
--sample
argument that sounds like it will do what you want.