VolAdj is/was available for 1.03 too, but it's a more involved job if you want to be able to switch it on/off or alter parameters, instead of just using the default value.
HiJack does a great job of encapsulating this.

Otherwise it's just a kernel image upload, trivial to do with Tony's Logo Editor.
The modified kernel is available here (the release 1.03 kernel for Mk1 and Mk2 players link)

/Michael