HAProxy community

Mix 2 method of balancing

Hello all!
Haproxy can balance traffic using http param:
balance url_param userid
if that param is new or absent than haproxy will use round robin.
Can I configure haproxy to use leastconn insead round robin with url_param balancing?
If there’s known user_id -> send request to known server
If there’s new user_id -> send request to server with least connection?