Multiple values for a single stored process parameter are provided as individual values with a numeric suffix attached to the parameter name. Here's a short code sample that can put the values together in the desired fashion, e.g., enclosed in quotes with comma separators.
/* EG generates this %LET statement. */
%LET eqnum=%NRSTR("10-1380"),%NRSTR("10-1428"),%NRSTR("10-1429");
/* SP parameters generate equivalent of these %LET statements */
/* when 2 or more values are supplied. */
%let eqnum1=10-1380; /* First selection */
%let eqnum2=10-1428; /* Second selection */
%let eqnum3=10-1429; /* Third selection */
%let eqnum0=3; /* Selection count */
%let eqnum=10-1380; /* Same as first selection */
/* Always anticipate first selection and number of selections. */
%global eqnum eqnum0;
%macro CombineEqNum;
/* Assumes SP parameter requires at least one selection. */
/* Additional logic required if zero selections is valid. */
%let eqnum="%superq(eqnum)"; /* Put quotes around first value */
%local i;
%if %superq(eqnum0) ne /* If counter is present */
%then %do i=2 %to %superq(eqnum0);
/* Append 2nd, 3rd value, etc. */
%let eqnum=&eqnum,"%superq(eqnum&i)";
%end;
%mend CombineEqNum;
%CombineEqNum
There is a more detailed explanation of the multiple value creation in the Stored Process Developer's Guide at
http://support.sas.com/rnd/itech/doc9/dev_guide/stprocess/input.html
There is a reminder that only the stored process server currently supports multiple values for a parameter. The workspace server only supports one value.