Script playing 2keyboards/ re-triggering right hand on other sounds

“I have two keyboards — AstroLab on Ch 1 (left hand chord) and KeyLab on Ch 2 (right hand melody). I want a Scriptlet where playing the right hand triggers both the right-hand note AND all currently held left-hand notes to the output. Both keyboards feed into the Scriptlet. Can anyone provide a working GPScript 5 Scriptlet for this?”