A B757-200 UNDERSHOOTS ITS ASSIGNED ALT WHEN THE CAPT'S ALTIMETER IS SET TO THE WRONG ALTIMETER SETTING S OF HAR; PA.

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WHILE CLBING TO CRUISE ALT OF FL350; WE WERE BEING GIVEN AN EXTREME NUMBER OF VECTORS; SPD CHANGES; AND TFC CALLOUTS. PASSING THROUGH APPROX FL310 WE EXPERIENCED SEVERAL SHORT BUT SEVERE CASES OF WAKE TURB FROM PRECEDING ACFT 12 NM AHEAD. THE AUTOPLT WAS ON AND THE CAPT (PF) HAD HIS FEET RESTING ON LOWER INST PANEL AND APPARENTLY BUMPED HIS ALTIMETER SETTING WHEN THE WAKE TURB HIT. THIS WENT UNNOTICED AND THE AUTOPLT LEVELED AT FL350 ON THE CAPT'S ALTIMETER. ATC CONTINUED ITS VECTORING AND SPD CHANGES AND THEN SHORTLY LATER QUERIED OUR ALT. THE FO (MYSELF) WAS IN MY NAV CHART AND EXPLAINING TO THE PAX THE WAKE TURB ENCOUNTER -- ANOTHER OF WHICH HAD JUST OCCURRED AFTER LEVELING AT FL350. WE THEN NOTICED THAT THE CAPT'S ALTIMETER WAS SHOWING FL350 WITH AN INCORRECT ALTIMETER SETTING; WHILE THE FO'S WAS SHOWING APPROX 300 FT LOW WITH 29.92 SET. ALT WAS QUICKLY CORRECTED WITH NO CONFLICT. WE OBVIOUSLY HAD OUR ATTN DIVERTED BY POSSIBLY EXTRANEOUS ACTIVITIES AND SHOULD HAVE BEEN MORE AWARE OF CAPT'S FEET IN RELATION TO INST PANEL.