You can select any drawing on a layout, right click and select 'Set as Autotext Reference'. Then when inputting your autotext you select 'Reference for...' from the drop down menu.
But for this to work you need to have an actual drawing on a layout to use as a reference, or perhaps it could be a small empty dummy drawing with nothing in it, solely for the purpose of referencing your autotext.
See more about it
here.
Cheers,
Link.