Create a text file named "ct.cmd" and containing this line:
@cleartool.exe %*
Save it into a directory that is included in %PATH% environment variable.
Now you can use the script from command-line, example:
c:\TMP>cleartool hostinfo
dunno1: ClearCase 9.1.0.4 (Windows NT 10.0 (build 19045) x64)
c:\TMP>ct hostinfo
dunno1: ClearCase 9.1.0.4 (Windows NT 10.0 (build 19045) x64)