Cannot control CacheItemPolicy properties from config file by noonand2

With reference to the System.Runtime.Caching class in .NET 4.0 it seems possible to only set a limited number of things in the configuration file to wit:
•name
•polling interval
•the amount of memory that that cache is allowed to consume
•the percentage of memory that needs to be hit before the cache will be scavenged

A sample section is shown below:

<system.runtime.caching> <memoryCache> <namedCaches> <add name="NameOfMyCache" pollingInterval="00:05:00" cacheMemoryLimitMegabytes="0" physicalMemoryLimitPercentage="0"/> </namedCaches> </memoryCache> </system.runtime.caching>

However it appears none of the really useful items (IMHO!) are controllable from the config file. These are the options that are all in the CacheItemPolicy class such as AbsoluteExpiration, SlidingExpiration and Priority (I can understand how the Callback functions aren't exposed although I would expect to see some options as to what to do in the event that these were called)

The question is, why is it not possible to do this from a config file or do you have to go away and roll your own custom sections?