corhavelaar

I'll try step by step :

Site A has alog lines, i assume linegroup 0.
Site A has VPN Trunk, i assume linegroup 1.
Site B has VPN Trunk, i assume linegroup2.

I assume you dial a 9 for external calls.

Set the following in Site A in the System -> telephony tab:
Dial delay time = 3000
Dial delay count = empty

Create system shortcodes :
SC = 9
TN = .
Linegroup = 0
Function = SecondaryDialTone

SC = [9]N;
TN = N
Linegroup = 0
function = dial

Create a shortcode in VPN Line 1:
SC = 9N
TN = N
Linegroup = 0
Function = dial

Set the following in Site B in the System -> telephony tab:
Dial delay time = 3000
Dial delay count = empty

Create system shortcodes :
SC = 9
TN = .
Linegroup = 0
Function = SecondaryDialTone

SC = [9]N;
TN = 9N
Linegroup = 2
Function = Dial

If you dial from Site A a 9 you dial tone and can dial the external number, the number will only be send to your linegroup if the Dial delay timer has exceeded.
If you dial from Site B a 9 you will get dial tone and you can dial the exteranl number, the number will only be send over the VPN line until the Dial Delay timer has exceeded. The complete number will arrive on VPN line 1 on Site A and because it starts with a 9 it will break-out over the linegroup 0 without the additional 9 you put in on site B.

If you wish to do it without secondary dial tone then do not make the shortcodes with the function secondary dial tone and omit the brackest in all other shortcodes.

Hope it helps you.