Actually I should rephrase this in another way. I assume the only thing that is being blocked is the Request Method itself as long as you are not using HTTP/1.0 Brute Force Login protection Bonus Custom Code and are not using any additional personal custom htaccess code that filters by empty/blank User Agents. Most likely all that needs to happen for the Host Monitor check to not be blocked is to remove HEAD from the Request Methods filter. So you do not “need” to do anything about the Server Protocol or the blank User Agent, but ask your Host if the Request is a HEAD Request. If it is then you would do this whitelist method in the link below.
http://forum.ait-pro.com/forums/topic/split-uptimerobot-whitelist-uptimerobot-bot/page/2/#post-8003