How to best convert CString to BSTR to pass it as an "in" parameter into a COM method?

I need to convert a CString instance into a properly allocated BSTR and pass that BSTR into a COM method. To have code that compiles and works indentically for both ANSI and Unicode I use CString::AllocSysString() to convert whatever format CString to a Unicode BSTR.

Since noone owns the returned BSTR I need to take care of it and release it after the call is done in the most exception-safe manner posible and with as little code as possible.

Currently I use ATL::CComBSTR for lifetime management:

 ATL::CComBSTR converted;
 converted.Attach( sourceString.AllocSysString() ); //simply attaches to BSTR, doesn't reallocate it
 interface->CallMethod( converted );

what I don't like here is that I need two separate statements to just construct the ATL::CComBSTR bound to the convertion result.

Is there a better way to accomplish the same task?