I have had success in electroporating HeLa and other cells, with
expression of cDNAs ranging from 2% (bad day) to 70% (good day).
Adherent cells are trypsinized then electroporated in suspension, so I
don't see why this wouldn't work with lymphocytes. Current Protocols has
a discussion on the subject. Conditions might approximate 300 Volts at
960 uF in a 4 mm cuvette.
Cheers, Alastair Mackay