Use the undocumented switch
/WRITECACHE:size_in_bytes
of the CACHE command to specify the maximum size of writes to be cached. The default value for this parameter is 65,536; the maximum is also 65,536.
Source: The OS/2 WARP Survival Guide
Use the undocumented switch /Dstg:on to get some more information and switches for CACHE.EXE. Use
CACHE /Dstg:on /?
to get a syntax help for the undocumented switches.
(WARP 4 only! but the switches /DirtyMax:n and /Writecache:n also work in WARP)
Source: Team OS/2 WEB pages