AFAIK, there isn't a way to do that.
You can experiment with the Photo Downloader's "Advanced" dialog -- maybe by creating subfolders based on custom groups and making the "Group Custom Name" a tag. That might at least allow you to select each JPG+RAW pair at a time for stacking, but that sounds tedious for stacking two images at a time out of 300....
I have given up shooting raw + jpeg, but here is what I did at that time:
Since you can't use version sets, I simply used the 'suggest version stack' feature after each batch import.
The search by visual similarity did a perfect job of grouping (stacking) pictures without looking at file names.
Note that if you 'get photos and videos by files or folders' you have an option to automatically suggest stacks.
As a workaround to reduce the "clutter" in the Organizer's display, simply hide the RAW files: search for the RAW extension to display only the RAW files, then select all of them and use Edit...Visibility...Mark as Hidden (Alt+F2).
You'll have to choose between stacks or hidden files : if you have stacks of raw + jpegs, you won't be able to select only raw files to hide them. Selecting by extension, you'll get not only the raw files but all other files in the stack with the 'non match' icons.
Intrestingly enough I do not understand why the same company makes products for the same tasks with completly different concepts for same features. The way I like to manage my workflow is to take jpeg+raw, then I would like to stack, go through the jpegs, make a album out of my selection and then work/ edit on jpeg or the raw (depending the type and ammount of work).
Regretfully I found that Lightroom does a great job of stacking automatically by capture time, hence stacking the jpeg+raw, which is great..but then when I go through my photos and tag them or move them to a collection, Lightroom works only on the top of the photo at the top of the stack, so when I go to my collection I cannot expand the stack and decide on which photos I rather work to publish or share. Now PSE10 does not stack by capture time, so you need to do pair by pair manually o try using the "image recognition functionality", but on the other hand when you are working through an album you can expand all photos in the stack...
I would love both functionalities in at least one of these adobe products,
1) auto stacking by capture time and
2) keeping the stack together across any view/filter
I have now spent last few weeks trying to see which product has the best workaround to decide which product I will keep as my standard or if I try to find a non-adobe product, for now I seemed to have found a plug-in from http://www.beardsworth.co.uk/lightroom/syncomatic/ which allows to automatically copy keywords and metadata within stacks in Lightroom allowing me to maintain the stacks together, but I think the PSE10 way to do it is much better..So you might want a try using lightroom, because I found no workaround yet for the autostacking in PSE10
See that note from John R Ellis about Lightroom and stacks being 'second class' citizens.
As I said before, I have given up using raw + jpegs. The only situation in which it was useful was when I had a wedding to shoot and I wanted to quickly show and share pictures with other guests.
Generally Lightroom has a lot of options to satisfy various categories of professional photographers, including many with no interest for me. (I have only version 3.6 of LR).
The main flaw with stacks in the Organizer is that once you have made a query including stacks, you find not only the 'close match' pictures, but also the 'non match' ones in the expanded stacks. So, you can't select, for instance, raw files only. And what it worse, is that it's the same problem with version sets.