Want to use call_procedure or call_function instead of execute

I've got a pseudo command line in a widget program set up something
like this:

case(event_type) of
'THIS EVENT': begin
         widget_control, input_field, get_value=command
         commands=strsplit(command, ', ', /extract)
         case(commands[0]) of
         'print': begin
                   ;print the variables listed in commands to a
widget_text field
         end
         endcase
end
endcase

The problem is that when I try something like

call_procedure('widget_control', output_text, /append,
set_value=commands[i])

the name of the variable is outputed to output_text, and not the value
of the variable.  Is there any chance of getting the value for the
variable (or the string representation of the value) without using
execute or a (very large) case block?

For reference, the working execute command would look like this:

result=execute('widget_control, output_text, /append,
set_value='+commands[i], 0, 0)

I also have a similar problem where a user may want to enter an exact
value into a field by means of an equation such as

3.0*!dpi/2.0

Any help would be welcome.

Braedley