Three observations while I think about this:

First, the key rhyme in the fragment is actually problematic, because "Lourdes" is properly pronounced with more of an "oo" (or "ou"; the source I checked cited the "ou" in "tour" as comparable). For purposes of the rhyme, it would be more accurate to refer to "herds" than to "hordes"...but that has an effect on the connotation that I don't know that I like.

Second -- and perhaps one of the reasons the fragment has remained a fragment for so long -- there's a significant tonal issue here. The source tune (and yes, it's clearly "We're Off to See the Wizard") is sprightly and brisk and cheerful...but the stories about Lourdes are deeply rooted in Catholic faith, and the two contrasting elements are difficult to reconcile in a way that avoids sounding disrespectful to the latter. [It might be noted, too, that the "Virgin of Lourdes" is arguably Mary herself, rather than St. Bernadette.]

Third -- if I end up with a complete lyric at the end of this (and I don't know that I will, but this sort of challenge is one I can rarely resist), I will almost certainly make one other specific change to the Houston fragment: "wonderful" will become "virtuous", which seems to me a far better word choice both for tonal purposes and to preserve the alliteration present in the source lyric. I commend that thought to anyone else inclined to take on the project.