일단 dll project를 하나 만드신 다음
만드신 form을 include하시고

BOOL WINAPI DllMain(HINSTANCE hinstDLL, DWORD fwdreason, LPVOID lpvReserved)
{
    if(BuilderForm == NULL)
    {
        Application->Initialize();
        Application->CreateForm(__classid(TBuilderForm),&BuilderForm);
    }
    return 1;
}
//---------------------------------------------------------------------------
extern "C" void __declspec(dllexport) TestBuilderFormView()
{
    BuilderForm->ShowModal();
}

부르는 쪽에서 static or dynamic으로 call하시면 되지 않을까요?

ex) dynamic call
hMod = ::LoadLibrary("BuilderFormView.dll");
    typedef void (*PFNTestBuilderFormView)();
    PFNTestBuilderFormView BuilderFormView = (PFNTestBuilderFormView)::GetProcAddress(hMod,"_TestBuilderFormView");
    BuilderFormView();