Venezuela visa - no proof of onward travel

I have a flight booked into Caracas next week, and the return is from Sao Paolo, Br. in January. We are planning to make our way down to SP via colombia, ecuador, peru, etc etc. BUT -- I have contacted the airline (TAP), who say i need to show proof of leaving Venezuela within 90 days for the visa, and I can't check in without it. (we're from UK by the way)

What is the best way to show this proof? Can I book Ven-Col bus tickets online anywhere? Do i really need to book a flight I don't intend to use, just to tick a box!? the problem is the duration of my return ticket more than anything else... If it were less than 90 days away the airline said it would be fine..

the idea had crossed my mind to forge a receipt for a bus ticket out of venezuela - does anyone have any sage couter-advice to this..? I'm not usually into being naughty haha, but surely there's a victimless crime right..?

any help is greeeeatly appreciated - we're (supposedly) flying on wednesday!
Thanks a lot
Harry