Unfortunately, this is bad advice... even though the SPK has a soft insert at the big toe, it is rather wide, high volume boot.  If he has a narrow, low volume foot his toe will smash into the front of the boot (insert or not) because the shape of boot does not securely hold his foot in place.  The soft insert is only a bonus feature to those who fit well into the SPK, not a cure-all for toe bang.  The same goes for a Booster strap- it only solves one cause of shin bang, namely keeping the tongue tight against your shin.  If he has a narrow, low volume foot he could very well get horrible toe bang and shin bang in an SPK with Boosters.
In short, do what everyone has said above... see a boot-fitter and buy the best option for your specific needs.