Anything you do that increases benefits will have to satisfy nondiscrimination.
You don't describe any of the circumstances that we would consider in dealing with this - amount/percentage of over funded status, number and ages of owners, if owner benefits are tracking at 415 limits, the relative number of employees/participants, how mature the plan is and whether the plan is aggregated with a DCP to pass testing or you have combined plan deduction limits that apply.
A joint discussion with the plan sponsor and investment advisor is warranted because a 21% return sounds great but at what risk and, if owner benefits are at or near 415, why construct the portfolio in that manner? This is a much different discussion if you have a $10M plan that just created $1.5M in excess versus a $1M plan that created $150,000 in excess.
Again, depending on particular circumstances, we usually recommend a number of alternatives, sometimes individually and sometimes in combination, including reducing future contributions, amending to increase benefits (usually a one-time balance increase, and possibly reducing contribution to CBP to offset additional PS contributions that are often needed to satisfy testing), paying eligible plan expenses from plan assets, and retaining a cushion for various reasons such as the 110% threshold to pay HCE lump sums or protecting against a down year in the business or the market (although ROR ICR does that for most part).
This is a good problem to have but the key is to not let the over funded position get out of control - but what constitutes out of control depends on the particulars surrounding the plan.
Good luck.