c# - Using Explicit Cast in an Extension Method

I have a weird problem when I'm trying to cast an object via an extension method. I have a class where I wrap some functionality around an IPAddress.

// Dumbed down version of class
public sealed class PrefixLengthIPAddress
{
public static explicit operator IPAddress(PrefixLengthIPAddress address)
{
return (address != null) ? address._address : null;
}
public PrefixLengthIPAddress(IPAddress address)
{
_address = address;
_length = address.GetLength();
}
private readonly ushort _length;
private readonly IPAddress _address;
}

I don't like the look of all the parenthesis to extract the IPAddress out of the object:

var family = ((IPAddress)prefixLengthAddress).AddressFamily;

I'd rather be able to do something like this:

var family = prefixLengthAddress.CastAs<IPAddress>().AddressFamily;

In order to do this I wrote the following Extension Method:

public static T CastAs<T>(this object value) where T : class
{
return (T)value;
}

Unfortunately with this I'm getting an InvalidCastException:

var family = ((IPAddress)prefixLengthAddress).AddressFamily; // Works
var family = prefixLengthAddress.CastAs<IPAddress>().AddressFamily; // InvalidCastException

I understand that in this particular case I could simply expose the IPAddress with a getter, but we also have more complex explicit casts that I would like to do this with.

EDIT

Thanks to Chris Sinclair's comment on using dynamic I have updated the extension method to look like:

public static T CastAs<T>(this object value)
{
return (T)((dynamic)value);
}

There is some overhead with using dynamic, but it is more than fast enough for my needs. It also seems to work with all the basic type casting I've tried.