I was doing some searching through JASNA's online journal and found this article written by Joseph Wiesenfarth in the Winter 2001 edition which suggests that the Insensible Charles from Jack and Alice was an early prototype for Darcy.

A couple of snippets:

• He compares Charles's first appearance at the masquerade where he dazzles all to Darcy's first appearance at the Meryton assembly:

  Mr. Darcy soon drew the attention of the room by his fine, tall person, handsome features, noble mien; and the report which was in general circulation within five minutes after his entrance, of his having ten thousand a year.The gentlemen pronounced him to be a fine figure of a man, the ladies declared he was much handsomer than Mr. Bingley, and he was looked at with great admiration for about half the evening. . . .

• Compares Darcy’s manners as being too much like those of someone who thinks everyone and everything revolves around him - like Charles:

  ...he [Darcy] was looked at with great admiration for about half the evening, till his manners gave a disgust which turned the tide of his popularity; for he was discovered to be proud, to be above his company, and above being pleased; and not all his large estate in Derbyshire could then save him from having a most forbidding, disagreeable countenance, and being unworthy to be compared with his friend.

  "I imagine my [Charles] Manners and Address to be of the most polished kind; there is a certain elegance a peculiar sweetness in them that I never saw equalled and cannot describe—.Partiality aside, I am certainly more accomplished in every Language, every Science, every Art and every thing than any other person in Europe.”

• Compares Darcy's mean opinion of the Bennets to Charles's of the Johnsons:

  I look upon you Sir to be a very good sort of Man in the main; a drunken old Dog to be sure, but that’s nothing to me.Your daughter sir, is neither sufficiently beautifull, sufficiently amiable, sufficiently witty, nor sufficiently rich for me—.I expect nothing more in my wife than my wife will find in me—Perfection.”