AFAIK there is no automatic way, but you can do it easiliy. Suppose you have created MyDialog with sources MyDialog.cpp/MyDialog.h:
- copy MyDialog.cpp/MyDialog.h to the new project folder
- copy wxsmith/MyDialog.wxs file to the wxsmith folder in the new project folder
- edit the project with a text editor and add the source files and the wxs
<Unit filename="MyDialog.cpp" />
<Unit filename="MyDialog.h" />
<Unit filename="wxsmith/MyDialog.wxs" />
- add in the wxsmith section the line associated to the resource, in this case:
<resources>
...
<wxDialog wxs="wxsmith/MyDialog.wxs" src="MyDialog.cpp" hdr="MyDialog.h" fwddecl="0" i18n="1" name="NewDialog" language="CPP" />
...
</resources>
You can use the original project as a guide.