Now, that said, I don't think it would be terribly unbalancing to introduce the following paragon feat:
Focused Initiate
Requirement: Level 11+, any multiclass feat
Benefit: Choose a multiclass initiate feat that grants you a power or ability (like Combat Challenge, Sneak Attack, an at-will attack power, or Healing Word). You upgrade the frequency with which you can use the power or ability granted by that feat. You can now use the power as often (at-will, daily, encounter) as that class can normally use. Thus, sneak attack becomes once per round rather than once per encounter and Healing Word becomes twice per encounter.
This feat would be no more powerful (and arguably weaker) than Versatile Master for half-elves.
DC