If you really really really want sustain.... you can buy something called a Fernandes Sustainer... I think a few other companies make them too... What they do is create a small magnetic pulse that pulls on the strings as the notes have been rung... this keeps the string vibrating for pretty ever... It's a neat little thing to install on a guitars. Or look into compressors... they compress the sound freuguencies and average them out... when the sound of the guitar starts to disappear the compressor compensates and keeps the notes ringing... but when the note dies completely so does the compression... Just a few things to look at... I could write a really long response explaining sustain and all the factors that go into it and all the mods that can be done to enhance it... But I don't have time right now... if you wish let me know and I'll post the information...