Please seek consultations on this, but indications are that deferred compensation would not be subject to the "earnings test".
From http://www.ssa.gov/pubs/10063.html :
If you get Social Security and your total yearly earnings exceed the limit and these earnings include a special payment [e.g., deferred compensation], you should contact Social Security. Tell us you think you received a special payment. If we agree, we will not count the amount of the special payment as part of your total earnings for the year.
From http://www.ssa.gov/OP_Home/rulings/oasi/43/SSR73-30-oasi-43.html :
Further held, such wages [deferred compensation], since wages, since earned prior to retirement, are not subject to the post-retirement work test and thus may not reduce the worker's retirement insurance benefits.
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