"Laver" is the greek word for "washing". So "laver of regeneration" would be the act of washing in baptism, or the matter/form. That is, the pouring of water and the form of the sacramental prayer.
So, "Laver of Regeneration" (matter/form) + Desire (proper disposition) = sacrament.
As, "Water" (natural means) + "Holy Ghost" (supernatural means) = sacrament.
Thus, you have to have both for the sacrament. Can you only have the desire? Sure. Will that justify you? It seems likely. Will you go to heaven only justified, but not baptized? Don't know.