Consider a site using wildcard subdomains and thus having thousands of "virtual" subdomains. What is the best strategy for submitting those thousands of subdomains to google via sitemap? Since google will not allow different subdomains in the same sitemap file, how would one proceed? Submitting thousands of subdomains by hand does not seem feasible. Thx!!
You have to make separate sitemap for all subdomain. You said thousand of subdomain so it would be tidy process to make sitemap for each subdomain manually. You can make it through programming. After completing all sitemap for all subdomain you can submit all in same google webmaster account in which your main domain sitemap is.