You should have that kind of structure of files:
├── control
│ ├── conffiles~
│ ├── control
│ ├── postinst
│ └── postinst~
├── control.tar.gz
├── data
│ └── etc
│ ├── init.d
│ │ └── myscript.sh
│ └── postinst
myscript.sh is the script you want to copy to /etc/init.d folder
remeber you can add poscript file to execute extra commands after install files on vu
after that go to cataloges and make archive:
cd control && tar czvf ../control.tar.gz * && cd ..
cd data && tar czvf ../data.tar.gz * && cd ..
finally you can make package myupdater.ipk
ar -r myupdater.ipk debian-binary control.tar.gz data.tar.gz
enjoy and comment!