*DOH* just noticed this question was a bit long in the tooth. Answer still applies, but is probably not particularly relevant any longer.
You can try to update them manually where the author hasn't updated their extensions, though they may or may not actually work.
If you've installed the extensions locally for your user (likely when using extensions.gnome.org), the extensions will be in
Within that directory will be one directory for each extension in the form extension@something . Within each extension@something directory will be several files, open the one named metadata.json. You'll see a line something like:
modify that line by adding ,"3.8" (or whatever version of gnome-shell you're running) to it:
"shell-version": ["3.6.1", "3.8"]
Save and repeat for each extension that doesn't work. Then logout/login. This will work so long as nothing else changed in the newer gnome-shell that the extension relied upon. This is not a given. IF there are any problems, remove your modification (just the part you added , not the whole line).