just worked out the rest of the internal IVBProjectEx interface:
interface IVBProjectEx_VBE
{
void Placeholder1(); // returns E_NOTIMPL
void set_ProjectName(string value);
int VBE_LCID();
void set_ProjectVersion(ushort wMajorVerNum, ushort wMinorVerNum);
void set_ProjectGUID(ref Guid value);
void set_ProjectDescription(string value);
void set_ProjectHelpFileName(string value);
void set_ProjectHelpContext(int value);
string get_ConditionalCompilationArgs();
void set_ConditionalCompilationArgs(string args);