Sorry, I don't have the answer. However, it looks like those base pads should work with the funnel. If not, see where they're making contact and file/sand down/trim/remove that part of the base pad. I did that to a 17 rounder....kept inserting, checking for fit and would then remove the mag and base pad and do a little whittling on the base pad...also had to use a little JB Weld on the base pad as there's a hollow portion in front....I filled the hollow portion full of epoxy, then did my skulpting.
Here ya go....a 17 rounder and a 20 rounder.
Here's the skulpted 17 rounder.
You could save some money by just modifying your stock plastic base pads. AND, they'll still work in a Q without the magwell flare...may look a little odd...so don't look at it. <img src="http://www.waltherforums.com/forum/images/smilies/biggrin.gif" border="0" alt="" title="Big Grin" class="inlineimg" />
OH, and if you use a 15 rounder, it'll disappear inside the magwell flare. I'd recommend modifying a 17 rounder. OR, just buy some of the +6 extensions.