Have you considered using UHARC instead of 7zip? It compresses better
Download all UHARC versions
What's new in version 0.6a
- option to create self-extracting archives (SFX / Win32 only)
- using again PMODE/W DOS Extender (does not need external program)
Note: UHARC 0.6a archives are compatible with v0.6 archives but
NOT compatible with any previous version (version number