Monitor webserver that need hostname in header not IP

So we have a few web servers in a pool and the application expects to see a hostname in the string, and the f5 just uses the IP Address of the node to do the query against, as one has to.

 

 

So how do I write a monitor query that puts in the expected host header but will use the IP Address to run the query against?

 

 

Oh and assume I don't know anything about HTTP, in fact assume I can't even spell HTTP.

 

 

Thanks

 

David.