currently, INSTALL PLUGIN always installs a plugin with all parameters having default values. It doesn't always work, for example InnoDB needs to know innodb_home_data_dir, otherwise it won't work. We will support parameters, similar to command line or server variables, in the INSTALL PLUGIN.
The syntax will be INSTALL PLUGIN pluginname SONAME "soname" [SET var1=val1[, var2=val2[, ...]]] ; the parser will put these name=value pairs into an array. The sql_plugin.cc will use my_getopt to parse this array and assign values to command-line parameters. On mysqld shutdown these values are lost, as SET values always do. One should use my.cnf for settings that should persist. Also we could re-read my.cnf on every INSTALL PLUGIN and pick the relevant options from there.