Lightroom :: Save Existing TIFFs With Zip Compression?

-I'm using LR 4.3 on a windows 7 x64 PC.

-I use one catalogue for each wedding/event/shoot.
 
-I import all my images as CR2 or DNG and work with these files in LR and Photoshop CS6.

-Once I complete the edits on a wedding, I'm left with , for example, 300 16-bit Uncompressed Tiff images in around a dozen different folders (I shoot big 600 pax + weddings sometimes).

-I want to: Re-save/Overwrite all these images as 8-bit Tiff images with ZIP compression.How can I do this?
 
-I've tried selecting all the images and Exporting them as 8 bit Zip Tiffs with the Overwrite Originals Without Warning tab selected. However I get the error that the file already exists and LR can do nothing about this.
 
-I've tried creating an Action in Photoshop but this poses two problems:

1) The photos are spread over multiple folders and selecting each one through File>Batch>Automate means the process requires manual intervention to reselect the next folder's tiffs - I want to hit the action, go eat lunch and come back to find them ALL saved.
2) The action acts outside of LR and I'd rather like to avoid 'metadata has been changed externally' errors although this isn't much of a biggie.
 
Why not just save the images as Zip Tiffs to begin with? I use a number of freelance retouchers , many of whom complain that the process of compressing slows their initial workflow (slower hardware).
 
(and yes - the space saved is considerable, where I live memory is still not quite cheap!)