Full credit goes to KINGMUZZAUK over on the UK equivalent of Cheapies, I found this on there and gave it a whirl here and it works massively reducing the face value of game pass.
First things first this does work but will require the use of a VPN to appear like you are in Brazil and following the steps properly. It also only works for new users that haven't tried game pass as it takes advantage of the upgrade to game pass offer. You also apparently need to not have an avtive Xbox live gold subscription.
Step 1: Buy the CD Keys codes for xbox live gold Brazil - $50.69 per year ($152.07 total)
Step 2: Log in to your chosen VPN (can be on a pc) and set your location to Brazil (I used PureVPN as I have a subscription but have seen others using Hola for free)
Step 3: In incognito mode redeem the codes against your account at redeem.microsoft.com (do not set auto renew on for the free month)
Once done you can shut off the VPN and go back to normal and your account should be showing xbox live for 3 years. Then upgrading to game pass using the $1 for 3 months trial offer on the game pass site currently upgrades any remaining Xbox live gold time on your account to game pass ultimate for free up to 36 months of value.
This last point is why you don't want to be adding the free extra months offered by auto renew, this will push you over the magic 36 month figure and means you won't be able to upgrade to game pass until you come back below that number.
Full thread I found this on is on HotUKDeals below:
https://www.hotukdeals.com/deals/xbox-livegold-12-months-sub…
The 36 months is the max (as you’ve said) but if you had ~7 months gold atm: buy 2x12 month codes - redeem first and turn on auto renew. Turn off auto renew and do the second (turn it on again when redeeming, then off again once redeemed).
You should now have 33 months, so buy the three months ultimate and that gets you to 36 (I think there may have been another month to auto renew here too).
NB - this is what I did (but with NZ gold codes) back during E3, so cant guarantee this is how it still works, but it should!