So... this is a smidge complicated. Might not be worth it (especially to the pros here) but thought I'd post it just in case.
If you sign up for Amazon Mechanical Turk to be a Worker, there are some receipt related data entry jobs/tasks you can do. The task themselves are irrelevant as there's generally better pay:time tasks available, but you can get some receipts from them.
You might have to accept the task and either complete it or return it OR you might be able to preview the assignment and just Skip for a new receipt. Not all receipts will be Walmart.
Once you've found the receipt with the item(s) you want on it, either scan it into your Walmart app or manually enter. Most (if not all) the time it'll say the receipt has already been scanned (since those various receipt scanning apps for $$$ outsource their work to mTurk workers) but it'll still show up in your purchase history.
Lift whatever items then take them to a diff store or come back another time, show receipt, get cash back.
Things to keep in mind:
Make sure the receipt scanned paid with cash (possibly debit card but cash is safest.)
Check the location on the receipt. These come in from all over the nation. If using a receipt from out of state and they look it over close enough you MIGHT have to make up an excuse (as simple as "on vacation" "just moved" "out of town for work" "visiting fam" whatever.) PROBABLY this wont be an issue since the receipt is on your phone anyways though. I've never had them look for anything other than the item (if even that), but more than likely they'll just scan the digital receipt then scan the item you're returning."
Not everyone can or will be approved for an mTurk account. Some may be flat out denied initially then months later randomly be approved. You can also be banned from mTurk by Amazon for too many poor quality work, rejections, and possibly Return HITs and/or you can also be banned from the individual task for the same reason. So if you HAVE to accept a task to see the receipt, please try to complete it per the instructions or return it as there is a huge potential for affecting the legit mTurk workers.