You don't need to go back to the drawing board, just set the global_vars option as quoted above:

If you want your variables to be global you can use global_vars option to new() described below.

From the docs:

global_vars - normally variables declared outside a loop are not available inside a loop. This option makes <TMPL_VAR>s like global variables in Perl - they have unlimited scope. This option also affects <TMPL_IF> and <TMPL_UNLESS>.