Assuming the numbers are proportionate, there's a 50% gross profit margin. I certainly see some room to play. However, I'm not sure if "software K", as you referred, is a big brand with millions of users, or is it something custom-made with much fewer clients? This matters in a number of ways.
If you want to structure through Belize, consider this:
1. Your basic minimum requirement is to pass the substance test. Rent or purchase property for the middleman company, and employ 2+ (my rough opinion) qualified staff to make it plausible that the Belizean company is a small regional software (re)licensing business.
Registering and maintaining a Belizean company is commonly offered at a price point of $1K or less per year, and it may seem like an easy way out. However, whenever you browse offshore service provider web sites, add another $50K per year to price tags, because only then you get what I call "a company according to a tax man". That $1K per year thing is paper trash.
Therefore, a Belize company alone costs $51K per year. Before you contemplate any further, make sure your estimated tax savings are higher than that.
Needless to say, you do not use slutty nominees who have their name everywhere, nor will you manage the company yourself from Mexico. Instead, you make the qualified persons you hired in Belize directors of the company.
2. On to more complex stuff. If you change your supplier, replacing the economic and cost-effective with an expensive alternative, you must be able to justify the economic reasoning; if it ever comes to Q&A with the tax man. It's not like you can just argue that the Belizean firm will give you a better quality product if the software license is literally the exact same thing.
Prep for the tax man Q&A:
One way around is to claim that it's no longer possible to acquire the licenses from the UK supplier directly. It's recklessly high risk, because it's not very difficult to verify that claim with the supplier. But if the supplier aligns his story with yours, it's an option to consider. The second way around is to make a claim that there are subtle differences in software which are nearly impossible to verify. Just modify the front-end a little bit, or have a freelancer developer do it for you. During an investigation, show the tax man both "versions of the software". As it appears, the custom-made expensive variant has more buttons and menu options on the interface, and therefore, it seems like there are more features (LOL). Tax officials lack the man power and qualifications to reverse engineer complex software for an in-depth investigation.
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Which ever back story you choose, you're exposed to risks; they are the highest during your first 3 years. Try to avoid an investigation in the first place. As Martin said, artificial profit shifting is not legal.
Lastly, perhaps the most important piece of advice I can give. My recommendation is to gradually make the license acquisition costs higher. Instead of jumping from $500 to $900 acquisition cost immediately, make it $600 on first year, then $750 on next. Settle on that $900 only after 3-4 years. It will look like an organic drop in profitability.
Good luck, you Mexican tax dodger.