No need to move away from the simple context; "he" is sanctified by the blood.
The context of Hebrews 10 will tell you this is true. That section of Hebrews 10 deals with "drawing near" or "drawing back".
Verse 22 says, "let us draw near with a true heart in full assurance of faith..." Verse 23 further encourages us to "hold fast" of our profession of faith without wavering.
Then at the end of the chapter, we are told not to cast away our confidence of faith and "draw back" for God has no pleasure to those who do. The "draw back" is a reference to those people who waver and leave faith and go back to their own works, ie leaving the covenant of grace and going back to the covenant of the law.
So, verses 28-30 are just dealing with someone who does that. The idea here is that if you leave the covering of the blood of Christ (leave the covenant of the promise) then there is nowhere to go for your salvation. Just look at the references to the law in those verses.
Verses 28-30 deal with the idea that if God dealt severely with those who violated the Law of Moses, then how do you think He would feel about those who purposely leave the blood of the new covenant?
The idea of someone leaving grace to "draw back" to the Law is seen in Galatians chapter 4 where Paul deals with people influenced by the Judiazers who wanted to move people back to the law. Paul says why would you want to go back to the weak and beggerly elements (reference to the law) and desire to go back to bondage. This same concept is highlighted in Hebrews chapter 6, verses 4-6. The writer says that if you leave repentance (ie, leaving your self righteous ways of approaching God and turning to His way through faith/grace of Christ) then there remains no more solution for your sin. If you leave Christ you're on your own and by the way you tread on His sacrifice and put Him to open shame.
So, it makes perfect contextual sense that in Hebrews 10:29, the reference to the gift of sanctification would be linked to a person (ie, "he") and not to anything else. Since the immediate context deals with "how much SORER punishment" will God deal out to the person who treated his Son's sacrifice this way. If God dealt severely with someone who despised Moses' law (verse 28) then how do you suppose God will deal with someone who despised the blood of Christ with which "he" was sanctified?