The only way to produce an Ivory is by using Yellowbellies or Ivories themselves. Lessers, Butters, Mojaves all produce a Blue Eyed Leucistic as their super form (or when combined with any other morph in whose gene lies on that allel). The super form of Fire is the Black Eyed Leucistic. Ivories are not a part of either of those gene complexes, so no, you cannot produce a Pastel Ivory by using a different morph.

That being said, a Pastel Ivory can be produced by any pairing that has at least one Yellowbelly gene from each parent and at least one parent with a Pastel gene.

Pastel Yb x Yb
Pastel Yb x Ivory
Pastel Yb x Pastel Yb
Pastel Yb x Pastel Ivory
Pastel Yb x Super Pastel Yb
Pastel Yb x Super Pastel Ivory
Super Pastel Yb x Yb
Super Pastel Yb x Ivory
Super Pastel Yb x Pastel Ivory
*Super Pastel Yb x Super Pastel Yb
*Super Pastel Yb x Super Pastel Ivory
Pastel Ivory x Yb
Pastel Ivory x Ivory
Pastel Ivory x Pastel Ivory
Pastel Ivory x Super Pastel Ivory
Super Pastel Ivory x Yb
Super Pastel Ivory x Ivory
*Super Pastel Ivory x Super Pastel Ivory

*Any of the Super Pastel x Super Pastel crosses will only produce Super Pastels, so no Pastels/Pastel Combos (like Pastel Ivory) will be produced. Snakes like Super Pastel, Super Pastel Yellowbelly, and Super Pastel Ivory may be possible though, depending on the the cross.

As long as those genes are present, a Pastel Ivory is possible.