New Yorker,
I don't think that portamento will help you, because that's the kind of feature that a trombone player would use (or a synth player like Keith Emerson in the "Lucky Man" solo).
Now that you mentioned Springsteen, I realize what you mean: the chords taken with the synth pad in that song linger for a long time because the release time of the sound was long enough. So it all comes down to programming the right patch that does not end too abruptly, I guess. A good reverb can help too.