Sprayed the wheel with soap/water. Big bubbles forming at the base of the valve stem.
I don't know what's the best thing to do in this case. Pulled the valve stem core and added another 35 to 40cc of the Bontrager TLR sealant, roughly doubling the original amount. Installed core and gassed it up. Shook the wheel. Now I could hear sealant sloshing. Shook the wheel, bounced it, etc. for a minute, trying to get sealant to splash against the base of the valve stem. Sprayed soap/water, bubbling stopped. Shook it some more, bubbling returned. So I brought the wheel inside the warm house and began sloshing it around every time I walked past it.
I'll keep doing that today and see what happens.
Thanks to everyone for their help!