Booster sent word today that he has released a software development kit for creating a custom PSP IPL. The SDK provides developers with a base set of code that will run independent of Sony's PSP firmware.
Download: http://exophase.com/files/psp/PSP_IPL_SDK_05.rar [Right-click, Save As]
He states that this is the 'basic model' which can work original codes without the SCE OS on the PSP. The release includes the source and examples of the PSP_MS_MULTI_LOADER.