what is the RIGHT(TM) way to configure background DHCP?

[deeptech71 at gmail.com]

as of recent times, on my network, the DHCP server takes a very long
time (>30s) to reply, slowing down the boot process. so i've decided
to put the DHCP client in the background (via rc.conf) during the boot
process.

attempt 1:
#background_dhclient="YES"
#background_dhclient_sk0="YES"
with this, the DHCP client isn't even started.

attempt 2:
#ifconfig_sk0="DHCP"
#background_dhclient="YES"
#background_dhclient_sk0="YES"
with this, the DHCP client is started, but there is a 30s waiting time.

(as if the background_dhclient and background_dhclient_<if> variables
had no effect.)

attempt 3:
#ifconfig_sk0="DHCP"
#defaultroute_delay="0"
this works, but looks hacky.

so what is the RIGHT(TM) way to configure a background DHCP client, and why?
are any of the DHCP-client-related rc.conf options redundant/useless?

btw, there is no example in /etc/defaults/rc.conf for ifconfig_<if>="DHCP"