It's not possible to split a license for one device across all devices in quite the way you are asking. Nor is it possible to renew for less than a year.
While it's not generally a recommended approach, what you could do is add a license using the 'add more devices' option, which is likely to push out the renewal date (remember that, in co-termination, that date does apply to all the devices) - but to move the date out any great amount you will need quite a lot of value in that license, to cover all those devices. I.e. it would need to be an expensive product or a long term, or both. You can use the License Calculator to evaluate what you might need: https://documentation.meraki.com/General_Administration/Licensing/Using_the_License_Calculator
Have you spoken to your Cisco account team? If you are remaining with Cisco technology for this requirement, or more generally, they may have more leeway to help you out on the commercials - i.e. still sell you a year of proper renewal licensing (this is definitely the best path here) - but at a more accessible price.
