Cable Girl,
I have no BTDT advice for you. But I do have a bunch of links I periodically post when I see a question like this (see further below). From everything I've read on wooing baby back, a relaxed atmosphere is critical. Catching them when they aren't too hungry is important which is why I think co-sleeping is a great idea.
I thought the "Re-birthing" technique (described in one of the links below) sounded a little wacky until I read a story about a woman who seemed to discover this technique by accident. Her husband coerced her into weaning her DD at 3 months and she really regretted it. Months later she was taking a bath with her DD when she reached up and playfully latched on. I vaguely remember a followup post saying that she went on to nurse her again. I have no idea for how long. As one or more of the article on this technique emphasize, safety is really important so you would probably want a "spotter" on hand just in case, but they would probably need to be unobtrusive.
Also, I did come across a recent thread on nursing in the bathtub. It alludes to some of the elements that might be conducive to wooing baby back: a womblike environment, warmth, relaxation, comfort, skin to skin contact, etc. I have included a link to this thread beneath the article on Re-Birthing.
I don't know which, if any, of these article deal with weak suck. But if you go to Kellymom and look you might find something a little more specific to that issue.
HTH, ~Cath
LINKS
Relactation and Induced Lactation Resources
http://www.kellymom.com/bf/adopt/rel...resources.html
Adoptive Breastfeeding & Relactation
http://www.kellymom.com/bf/adopt/index.html
Relactation and Adoptive Breastfeeding: The Basics
http://www.kellymom.com/bf/supply/relactation.html
Help -- My Baby Won't Nurse!
http://www.kellymom.com/bf/concerns/...to-breast.html
Re-Birthing: Help For Latch On Problems
http://www.lactationconsultant.info/rebirth.html
MDC link to thread on Nursing In The Bathtub
http://www.mothering.com/discussions...ighlight=water
When a Baby Refuses to Nurse
http://www.mobimotherhood.org/MM/article-refusal.aspx
Helping a Mother with a Baby Who Is Reluctant to Nurse
http://www.lalecheleague.org/llleade...tNov99p99.html
My Baby Just Doesn't Get It
http://www.wiessinger.baka.com/bfing...e/babyget.html
~Cath