One way could be to use the convolver to add an impulse response for the echo profile you're after:
http://code.compartmental.net/minim/javadoc/ddf/minim/effects/Convolver.html

I've not done this in minim myself, so don't know how it performs, but have used a similar process in octave. Generally speaking though convolving can be slow so this may not be effective if you're after a real-time effect.

You can get various impulse responses from the web, or could build your own response signal

If you're not stuck with minim for your audio then Beads comes with a delay effect.