Definir o parâmetro CacheControlMode conforme descrito na documentação do IIS7 deve ser feito o que você quer:
To set the expires response header to expire content periodically and to set the number of seconds, minutes, hours, or days at which to expire the content, use the following syntax:
appcmd set config /section:staticContent /clientCache.cacheControlMode:UseMaxAge /clientCache.cacheControlMaxAge: timeSpan
The variable timeSpan is the time at which to expire the content. The format for timeSpan is d.hh:mm:ss, where d is the optional number of days, hh is the number of hours, mm is the number of minutes, and ss is the number of seconds at which to expire the content. For example, to set the cache to expire every two days, type the following and then press ENTER:
appcmd set config /section:staticContent /clientCache.cacheControlMode:UseMaxAge /clientCache.cacheControlMaxAge:2.00:00:00