I know foobar will convert multiple flac files to a single image (there's a recent post relative to this - but there a cue sheet already existed), but I need a faster way. I have live shows that currently exist as individual flac files for each track (about 400 folders on a hard drive, each folder titled name of the band and date of the show)

To make my organization a little neater, I'd like to combine them into one image (maintaining integrity of the original files, e.g. gapless playback), and create an external cue sheet I can fill in if I please.

What would be money is if whatever program could read the directory name and insert the name of the band into the "Artist" field and date into the "Album" field, but that's probably wishful thinking.

with foobar2000, the key to this batch conversion process is the existence of ALBUM tags
no pre-existing cue sheet is needed

(1) If the files are not currently tagged, use foobar's masstagger to get the album info from the files' directory name (and you might as well mine any other data contained within the path/filename)

(2) Select all files to process, Convert -> Convert to Album Images with Cuesheets ...

edit:
the gapless playback concern doesn't apply here since you're dealing with lossless FLAC
*unless the files are broken to begin with, and don't align with sector boundries?

You could try shntool. Use the join command to join the files and the cue command to create a cue sheet. Don't delete the original files until after you have created the cuesheet.