Google Dynamic DNS Wildcard Subdomains
Solution 1:
The trick is to create a Synthetic Record for a any subdomain other that *.
Create the synthetic record for wildcard.domainname.com instead of *.domainname.com.
Then create a CNAME record (not synthetic) of the subdomain *.domain.com and point it to your synthetic records subdomain wildcard.domainname.com.
The placeholder subdomain wildcard could really be anything.