What you seem to want is something like the ability to "inject" named constant values into the DLL's typelib, e.g.:

Code:
    [
        helpstring("Global constants.")
    ]
    module Global
    {
        const double Pi = 3.141592653589;
    };
Even if you managed this somehow you'll likely get garbage for the value. The problem is that the MIDL compiler does not support floating-point values here even though you get no compile error.

double attribute

Remarks

The double type is one of the base types of the interface definition language (IDL). This type can appear as a type specifier in typedef declarations, general declarations, and function declarators (as a function-return-type specifier and a parameter-type specifier). For the context in which type specifiers appear, see Interface Definition (IDL) File.

The double type cannot appear in const declarations.
The same goes for float (Single).