I think the underlying methodology is subject to scrutiny. If it is really a matching formula, then you have a contingent rule violation, because it isn't legally a match.
Rather than advise you to re-read 404(o), I suggest you talk to a pension actuary who specializes in these small plans. That actuary may also advise you that the point of this plan (BTW, your client is the perfect candidate) is not to maximize investment return, but to maximize the deduction. Use a DC plan for aggressive investment strategy.
415(b)(5) provides that the maximum annual benefit is prorated for less than 10 years of participation. In the first year the maximum benefit he can accrue is 1/10th of the annual dollar limit.
If your plan document provides for discretionary contributions allocated in a discretionary manner based on criteria broad enough to include (e.g., "any basis acceptable to the employer,"), sure this is OK.
This sounds familiar (crazy talk from the janitor who answered the phone at the IRS). I can tell you what I would do - start filing under the correct number and reference the old number where it asks.