Probably can be done if you know how to use HTTrack via the command line.

Then you could build a .BAT file to execute the commands so that it goes to
<http://This.Is.The.First.Site.com> then <http://This.is.the.Second.Site.com> and
so on.

If you're not familiar with .BAT files, you'll need to google for them and
learn. You might be able to copy & paste the command line options from the
WinHTTrack logs.

I'd place Limits on the download (like 10 or 30 seconds) then try a .BAT file
that calls 5 or 6 httrack sessions. watch the folder where they download and
see if they're done in order (they should be).

Then once you're satisfied, remove the Limits and let them
go.

from <http://www.httrack.com/html/fcguide.html>

Limits options:
  rN set the mirror depth to N
  mN maximum file length for a non-html file
  mN,N'                  for non html (N) and html (N')
  MN maximum overall size that can be uploaded/scanned
****  EN maximum mirror time in seconds (60=1 minute, 3600=1 hour) ****
  AN maximum transfer rate in bytes/seconds (1000=1kb/s max)
  GN pause transfer if N bytes reached, and wait until lock file is deleted
  %eN set the external links depth to N (* %e0) (--ext-depth[=N])
  %cN maximum number of connections/seconds (*%c10)



Setting limits provides the means by which you can avoid running out of disk
space, CPU time, and so forth. This may be particularly helpful for those who
accidentally try to image the whole Internet.


httrack <http://www.shoesizes.com> -O /tmp/shoesizes -r50