Your answer is: Logic Audio Platinum.
This is you vocal track in the multitracker:
You want the last few words to echo but you want the delaying effect to mix in smoothly with the original track.
Logic lets you plunk in a DX plugin into a separate BUS channel on the mixer. And in each mixer channel there is a BUS knob.
So if you set the knob to a certain degree, channel gets wet with the delay.
Now the beauty of Logic Audio is that you can automate these BUSes. Somehow it lets you record your movements on this BUS knob in MIDI language(to a midi file?).
So after that, all you have is the dry vocal channel in a wav format. + you'll have a MIDI channel active which is the recorded BUS automation information.
And on playback, the vocal channel's signal is processed according to how you recorded the automation.
I hope this helps.
I found Logic being a very CPU hog. It was a little jittery on my machine during some parts but I would trust it as being my fully functioning multitracker/processor/mixer/etc.
although I do have a Cel400, and a really slow Quantum 5700 HD.