"BLF" & HINT for dialplan feature

I am running Asterisk v1.4 (IAX2 trunk, TDM400p with 1 FXO, 2 FXS, 1 SIP extension) and have an Aastra 9133i with the latest firmware (v1.4.2).

Within my dialplan, I have written the following such that on any incoming call through my FXO port, not only are my internal extensions notified, but I have also added logic so that I can control whether my mobile is also notified (find me/follow me with CID). This is done with the following logic:[incoming] exten => s,1,GotoIf($[${EC500} = true]?true_EC500:false_EC500) exten => s,n(true_EC500),Dial(${9133_K}&${ZAP1}&${MOBILE},20,o) exten => s,n,Goto(end) exten => s,n(false_EC500),Dial(${9133_K}&${ZAP1},20,o) exten => s,n(end),VoiceMail(u501@default) exten => s,n,Hangup()
With my $EC500 variable, I have the ability to control when calls are forwarded to my mobile.

What I would like to do is to be able to display via BLF on my Aastra 9133i the status of the forwarding (value of EC500). Likewise, when I press the associated feature button, I want to initiate a state change (i.e. true to false, false to true) and have the BLF reflect the new state.

Is there any way to subscribe to a variables state with the HINT command? Is there another way that I could do this?

many thanks,