Venmo appears to be pretty reversible to me.
According to their
fees page, you are able to fund transactions with your bank account as well as your credit/debit card, which makes receiving payments very reversible for a long time after the transaction (measured in months).
I would suggest that you withdraw the money in your Venmo account to your bank account and then use a cash type method (eg cash in mail, Western Union, Walmart-2-Walmart, cash deposit) to buy your bitcoin