Need Fax Modem to stay off hook longer when sending international faxes

When I fax to third world countries, my fax modem goes on hook just before it receives a handshake tone from the receiving fax, which is after around 35 seconds.  I cannot seem to find a setting to adjust this default.  As a result, these faxes need to be printed and sent over a manual machine.

Can anyone advise me on this one?

Thanks!