hmm i cant think of anything why it shouldnt work. map into mem, resolve imports etc, jmp entrypoint. actually this wouldnt be much different as writing an loader stub for an pepacker. only problem might be relocation info. since .exe files normally use an std imagebase, reloc infos are stripped, without them you might have an hard time figuring out what actually is an offset and whats code.
an solution to this might be to compile the "loader" app onto nonstandard imagebase so the 0x400000 range is "free" (but then again how to alloc mem on exactly this address), or compile the "target" app with relocation info u can use.