You could use these options
git.exe /VERYSILENT /COMPONENTS="icons,ext\reg\shellhere,assoc,assoc_sh"
I was able to piece together the options from looking at the code here: https://github.com/msysgit/msysgit/blob/master/share/WinGit/install.iss
Also, the commands for inno setup can be found at: http://www.jrsoftware.org/ishelp/index.php?topic=setupcmdline