He has vague ideas of using the cabinets himself, somehow. Maybe getting Hermione out, if push came to shove. But what if Borgin were right there, standing in the middle of his own bloody shop, when Draco did? Aside from the obvious problem of Draco stepping out of a vanishing cabinet with Hermione Granger, it would alert everyone far and wide that the cabinets were fixed after all. No, waiting until summer is still his best bet.