Allow Changing Slow Start Threshold Default Value

We are currently planning to introduce IIDR (IBM InfoSphere Data Replication) for IMS in our system.
The IIDR capture server resides in main site and the IIDR apply server resides in disaster recovery site.
These two sites are about 500 KM apart and there is planned to be about 30 msec delay in RTT in the network.
With the help of Michael Fitzpatrick, SME in this area, we conducted tests in test environment using WAN emulators to emulate delay.
From the test results we confirmed that the throughput (using TCPIP) was low (compared to our target throughput) because of slow increase in congestion window due to large RTT (=30msec). (It took about 15 minutes for the congestion window to hit the ceiling)
By using a SLIP developed/tested by Mike, we changed the slow start threshold. By changing slow start threshold we could confirm thatthe congestion window quickly rises and hits the ceiling in about 20 seconds resulting in improvement of throughput.

This function to change slow start threshold default value is required to meet our target throughput.
Our request is to have a more formal way of changing start threshold other than using SLIP. (for example setting by parameter)
We have already discussed on this point with Michael Fitzpatrick so it will be helpful if you can involve Mike in this RFE.

Current production system OS is z/OS V2.1, so we would want this function made for z/OS V2.1.