Looking at some of my players and the NT I'm coaching (the dreaded Korea), that wouldn't even be far fetched to give +1 in skill wherever you want for each +1 in XP. None of the 31 y old (or less) are above 7 in XP. I think those players could survive with +6 in their skills while not throwing overboard the balance.
The additional skils would have to be used on the X lowest skills (included FT/ST). The free skill would not be +1 exactly, it would allow you to reach the next level of a skill. For example, if you have 5.7 in Passing and you put your free skill there, it becomes 6.0, not 6.7. Bit of a gamble if you don't follow your players skills or don't know them (purchased players).
I might be saying stupid things, but that's a start from where someone can propose something else.
Maybe make it an inverse rule based on the level of the skill... A formula such as 1/skill level x 5
So a skill of 20 would only go up .25 but a skill of 5 would go up 1.