Create a custom dialogue with a combo box. In the properties dialog box for your combo box control, insert a variable into the text box for the "Combo Box Text" property, e.g. %ITEMSFORCOMBO% . Then, before presenting the custom dialogue, set ITEMSFORCOMBO to contain the desired items. Each item must be separated by a %CRLF%. For example, to present a list of exe files to upgrade, set
%ITEMSFORCOMBO% to
%FIRSTEXE%%CRLF%%SECONDEXE%%CRLF%