AT chars in dial string

Good day

Using a class 1 modem.  The standard AT command for dialing is ATDT%s.
This is not changed in the config file.  In some cases, depending on the
number, I would like to add a W to the dial string to ask the modem to wait
for a dial tone and in some case not.  This would make the dial command
ATDTW%s. I cannot add it to the number as the default dial rules change it
to a 9, and then there are checks to make sure the number is only digits.

Is there any way around this?

Kind regards
Christo