I managed to solve it 🙂
Please note that I don't use products but only one subscription type, which opens up a bit more flexibility in terms of a quick purchase process if you are a bit creative.
Basically the idea is to set up a page (in pages) with two different subscriptions in the front of the flow that looks like this:
Each checkbox effectively generates an invoice of a specefic subscription. (The select is to promote the preferred route...)
I am aware that this implementation has it's downsides, but it's what works best for me.
Here is the code that is behind every checkbox (and the select button) to make it possible to subscribe though it 🙂
<a href={url="app=nexus&module=subscriptions&controller=subscriptions&do=purchase&id=<SubscriptionID>" csrf="true"} alt="Subscription">
Some things to watch out for:
Do not add those options to the paymentForm for guests... Clicking the button generates a new invoice, guests will be required to re-enter their details as that is invoice based. (It works well for registered users though). This was the reason why I created an extra step.
Do not have more than one payment method active for a subscription where you use this method. Otherwise people will have the option to chose between these later which is messy.
Add the page where you sell it to robots.txt to prevent google from crawling the links (prevents some invoice spam 🙂 ).
Be aware that users might drop off with a higher price.
A user can only have one active subscription at once, otherwise things go kaboom... (I have an access check in place to prevent subscribers from accessing the buy button 🙂 ).
IPS will obviously not support this 🙂 Use at your own peril.
I do not recommend implementing this if you do not know what you do. Tinkering around with billing systems can definitely either improve your bottom line, or simply ruin it if you screw up (Both technically and legally).