[Asterisk-Users] disable transfer on outgoing calls?

[tad]

hi there. i'm developing a kind of collaborative phone system in which
groups of users need to navigate phone menus together, and run into
problems with the '#' character.

here's a scenario:
1) person_a dials into my asterisk server.
2) asterisk parks the call, and initiates an outgoing call to person_b
3) after verifying person_b (by requiring a keypress), asterisk bridges persons_a&b.
4) person_b initiates a 3-way call to some_phone, which is an
automated menu-driven service developed by someone other than me.

currently, i have all this working. however, i encounter difficulty if
some_phone asks the users to enter '#' - asterisk interprets this as
'transfer', and things go horribly wrong.

i know that the 'Dial' application allows me to disable the transfer
function, in which case asterisk ignores '#' (i've tested steps 1,2&4
of the above scenario using 'Dial', and confirmed that it works). however,
i can't seem to figure out how to disable transfer for outgoing calls that
are initiated through the Manager interface (or through .call files, for that matter).

i've checked the manual, wiki, and google, and so far have come up empty.
i have also looked at several source files, but am - frankly - a bit overwhelmed
by them ;)

does anyone know of any easy way to do this, or have a pointer
to more detailed documentation of how outgoing calls work than i've been
able to find at the above references?

also, in case you're wondering, i can't simply use the 'Dial'
application because i need to verify callers (step 3 in the scenario)...
at least, i don't think this is possible with 'Dial'.

thanks much,
tad