Another trick is my eBay account. It's a separate, sacrificial account that's just for eBay, mine alone. So as long as you sell stuff to fund the account, you can use your bank account credit card to buy whatever you want. Every once in a while a little refund or rebate check finds its way into it.
Another trick is to do a horizontal upgrade, like an AVA T7 preamp to an Ultra preamp. Only the most discerning eye would ever see the difference. Doesn't work if you're moving from bookshelf speakers to floorstanders.
And playing dumb like a fox can help. Once I bought new Coda cranks for my Cannondale. When my wife asked if I had bought new pedals, I could honestly say, "why no, dear."
Am I gonna fry in hell?
Paul