JAM scripts and Altera's USB-Blaster cable

Hi everybody,
I use a script written a long time ago to play with the JTAG interface
of a custom-made circuit (in FPGA).
The JTAG interface is soft (i.e not the Altera's one but implemented
using FPGA's logic).
In the past I used the JAM/STAPL player and every thing was ok.
Later I bought an Altera USB-Blaster cable. I was surprised to
discover that the JAM player didn't support it. After some
investigations I found quartus_jli.exe, which can play them on the new
cable.
The issue is that it seems that it doesn't support the FREQUENCY
command.
The problem is that my custom-made JTAG interface is very slow.
Is there any other command or method to set the JTAG frequency?

Cheers