Once you have got used to the imagebuilder, it is so quick and simple to make a new image that it is not worth bothering trying to hack an existing image. Also the imagebuilder compresses everything into the image saving a lot of space compared with an image you have installed many packages on top of.
You can use opkg to list everything installed using
echo $(opkg list_installed | awk ‘{ print $1 }’)
The output is perfect for the make command line.