Source or Import servers into backend

Help!
1

I am using HAProxy as a forward proxy gateway to 1000 of upstream proxy IPs. For testing it works as expected like below -

 backend py_proxy
	cookie SERVERID insert indirect nocache
	option httpclose 
	option forwardfor header X-Client 
	balance leastconn 
 	mode http
    	option httplog
  	use-server %[req.hdr(proxy-serv)] if { req.hdr(proxy-serv) -m found }

	server srv1 104.167.24.160:3128 check inter 10s
	server srv2 104.207.36.222:3128 check inter 10s
	server srv3 104.207.32.214:3128 check inter 10s

I am looking for any technique to add those servers from a file. Because scripting of thousands of servers in config file is not a good idea. Any help ?