If you bought him for $100m, you don't really have to worry about an insane salary, do you? I mean if his only other option is the KHL, because OP says you'd "own his rights", then I guess you can pay him league minimum unless he threatens to retire.
So I guess this is one of the reasons why the league needed a union in the first place.
I interpreted the question as that you're basically buying pick #0, jumping the line to draft somebody (value decreases a bit if you're losing your first round pick, so just assuming you buy pick #0).
So basically you control him until UFA (no different than anybody else) but may have to pay the max contract each year (you're not forced to, but imagine buying a guy for $50M and losing him on an offersheet? so you'd need to budget spending to the max). So every year you'd have to be willing to pay him up to $16.3M (20% of cap right?) or maybe he gets an offer sheet.
I don't think you could control how much he makes, sounds illegal/PA wouldn't allow it/etc so he'd need to follow the same rules as any other draftees. NHL + teams may also want a rule that they would also have to agree to refund money if the player leaves for another league/NCAA (but rules to make sure the team isn't screwing around - ie player refused a bonafide max contract).
If it was only once a year, and only one team in the league could do it (and maybe you'd need a 5-10 year cooling off window for each winner) ... I could see Bedard getting north of $50M for this being the first year. If this had been in place for several years, I doubt he's bought for over $25M.
Instead of making the maximum on an ELC (roughly $4M?) I think the person should also be entitled to a signing bonus or higher salary during the ELC. Maybe double the ELC max with bonuses, or the bonus is a % of the auction.
