setting subvar to the value of another subvar in maxl script

Gurus,

I am trying to set the value of one substitution variable to the value of another substitution variable in a maxl script but cannot figure out how to do so.  For example, I have a subvar called &BudgetYr which is set to FY14. I want to set this value to the subvar &ForecastYr.  Currently in the script, I have to set this value manually for ForecastYr. I have tried other methods but am not able to get it. Please help.

login admin ********* on essbaseserver ;
alter database EssCube.Plan1 set variable ForecastYr '"FY14"';
spool off;
logout;
quit;
exit