Problems with APEX_ITEM.CHECKBOX

I am trying to control the checkbox on a report in APEX.  Everything works perfectly until the list of checkbox entries exceeds 4000 characters.  I believe this is due to a limitation that varchar2 can only be 4000 max in an SQL. 

I pass the list of checked items into APEX_ITEM.CHECKBOX via an application variable called F118_CHECKBOX_LIST. However, I have also tried changing that to a separately defined variable of FCHECKBOX varchar2(30000).  That failed to work as well.

Example query for report:

select APEX_ITEM.CHECKBOX(1,
inv_key||','||inv_type_key,
'onchange="spCheckChange(this);"',
:F118_CHECKBOX_LIST,