Problem to make blind transfer on external calls where 2 dialing stage have been used

seems that the blind transfer works fine with internal extensions.
but when a external call is made blind transfer it is not reconized the code. but between internal or incoming external calls work fine.

so if one external incoming call arrives it accept the transfer code but when i dial out with gsm gateway. two dialing stages 33383336p90381278451
being p the pause for two stage dialing. when the external outtbound call is made and want to transfer the call to park slot it does not recognize de code blind transfer

2b how can I make a script or something to automatize the blind transfer each 4.5 minutes automatic ???
that way I can save time and money dialing codes each 4.5 minutes
the timing script is because one of my extensions is a gsm gateway. and my gsm card allow first 5 minutes to be free. so if I hang up each 4.5 minutes the call goes and goes for free

any info that drive me in the right direction would be so much appreciated thanks