Setting up HAProxy 1.5 to use map to match acls to backends

Help!
1

Basically, what the title says. I’d like to use a map file to simplify the haproxy configuration file. Currently the frontend and backend sections of the configuration file look like this:

frontend http
  maxconn 2000
  bind 0.0.0.0:5000

  acl test_service-webserver path_reg -i /service/test_service/.*  
  use_backend servers-test_service-webserver if test_service-webserver  

  acl test_service-rest path_reg -i /service/rest/test_service/.*  
  use_backend servers-test_service-rest if test_service-rest  

backend servers-test_service-webserver  
  balance leastconn  
  cookie TESTNAME insert  
  http-request set-header X-Forwarded-Proto https if { ssl_fc }  
  server servername1.intranet.com 127.0.0.1:9000 cookie S1 check inter 30s fall 1 rise 1 

backend servers-test_service-rest 
  balance leastconn  
  cookie TESTNAME insert  
  reqrep ^(.+)\ /service/rest/test_service/(.*?$) \1\ /\2  
  server servername1.intranet.com 127.0.0.1:9001 cookie S1 check inter 30s fall 1 rise 1

This is the basic syntax, though in the real case, the configuration has several dozen acl with corresponding backends, making maintenance somewhat painful.

My idea is to extract the ACLs into a separate map file, meaning that instead of having several hundred ACLs, the configuration file will have one line that will check for the required path in the map file, and then look for the related backend name to route to:

haproxy.cfg:

frontend http
  maxconn 2000
  bind 0.0.0.0:5000

  use_backend bk_%[base,map_beg(/apps/haproxy/config/haproxy.map)]

backend servers-test_service-webserver  
  balance leastconn  
  cookie TESTNAME insert  
  http-request set-header X-Forwarded-Proto https if { ssl_fc }  
  server servername1.intranet.com 127.0.0.1:9000 cookie S1 check inter 30s fall 1 rise 1 

backend servers-test_service-rest 
  balance leastconn  
  cookie TESTNAME insert  
  reqrep ^(.+)\ /service/rest/test_service/(.*?$) \1\ /\2  
  server servername1.intranet.com 127.0.0.1:9001 cookie S1 check inter 30s fall 1 rise 1

haproxy.map:
http://servername1.intranet.com:5000/service/test_service/ servers-platformbot_faq-webserver
http://servername1.intranet.com:5000/service/rest/test_service/ servers-platformbot_faq-rasaserver

So far, I have not been able to make this work, receiving only 503 errors when going to the http://servername1.intranet.com:5000/service/test_service/home, when it should map to the webserver backend. Is what I’m trying to do possible with HAProxy 1.5? If not are there any other workarounds? I realize that 1.5 is EOL, but I am limited to it due to my organization not upgrading.