Three ways to boost sustain (without improving your technique or spending much):
1) overdrive/distortion
2) compression
3) feedback: facing the speaker (at close range) and/or just playing very loudly
The guys on youtube were probably using all 3, but Hendrix, for example, got by on 1 & 3 alone. I'm assuming that you're using some overdrive already. Try getting cozy with your amp and see what happens.
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