I think there's one more way. I didn't test it, because I lack the WRT3200ACM. But if you are interested you could check it out. However, you have to be aware that this is your own "configuration"... and it might break someday. nobody can guarantee it that it works or you can keep it forever the same.
The general idea is to use the ieee80211 hotplug triggers to edit the configuration, instead of using uci-defaults. I've seen scripts for ipq806x updating the wifi MACs. So, it isn't a new hack.
In order to use the hotplug triggers, you only need to put a executable? file into /etc/hotplug.d/ieee80211
and name it like 20-myconfig or something. The important part is the number, it has to be higher than the script which calls "wifi config".
now, in your script, you simply monitor if the default_radio2 network do exist, if it doesn't you can exit.
But if the is there you check for default_radio2, you know that the "wifi config" script has just created the initial configuration. now you your modifications and rename the default_radio2 node in to process to something else.
Here's an example, that might work for you:
[ $(uci -q get "wireless.default_radio2") ] || exit 0
uci -q batch << -EOF
uci -q commit wireless
(The /sbin/wifi at the end is a bit questionable, since it will retrigger the scripts and enable the wifi.
But on the second time round, the default_radio2 would be renamed, so it will exit.)