Check HAProxy servers through http or socks proxies

Question

How can I check a server by use proxy in HAProxy? I mean, I can curl someurl.com through an http proxy like this:

curl -x 127.0.0.1:8080 someurl.com

My question is when I config HAProxy to check destinations, how can I use something like the '-x' flag? Something like this:

listen balancer
    bind :9000
    option httpchk GET /
    http-check expect status 200
    server server1 someurl proxy 8080 maxconn 100 check

Is there any option to do that? Plus, about socks protocol.