edit Sadly not!
Sounds like you can theoretically do the old Xbox game pass trick of loading up Gold and then upgrading.
£25 for an annual standard plan, and then upgrade to Ultra. First 2 months free, so potentially 14 months for £25 (then £18.99 a month after). No idea if this works in practice!
"If you upgrade, your plan will be active immediately, and the remaining time on your current plan will be credited towards your new plan."