I have been working on this problem recently and found a lightweight workaround with pkzip. I start pkzip with shellexec() and start a loop trying to open the zip file for read/write access as follows;

lnfh=0
DO WHILE lnfh <= 0
INKEY(2)
lnfh=FOPEN(tcZipFileName,12)
ENDDO
FCLOSE(lnfh)
Works for both zipping and unzipping using PKZIPC.EXE