Storing UTF-8 string in a UnicodeString

In Delphi 2007 you can store a UTF-8 string in a WideString and then pass that onto a Win32 function, e.g.

var  UnicodeStr: WideString;  UTF8Str: WideString;begin  UnicodeStr:='some unicode text';  UTF8Str:=UTF8Encode(UnicodeStr);  Windows.SomeFunction(PWideChar(UTF8Str), ...)end;

Delphi 2007 does not interfere with the contents of UTF8Str, i.e. it is left as a UTF-8 encoded string stored in a WideString.

But in Delphi 2010 I'm struggling to find a way to do the same thing, i.e. store a UTF-8 encoded string in a WideString without it being automatically converted from UTF-8. I cannot pass a pointer to a UTF-8 string (or RawByteString), e.g. the following will obviously not work:

var  UnicodeStr: WideString;  UTF8Str: UTF8String;begin  UnicodeStr:='some unicode text';  UTF8Str:=UTF8Encode(UnicodeStr);  Windows.SomeFunction(PWideChar(UTF8Str), ...)end;