The only conceivable way would be to write all your SS 2.0 as Suitelets and then call them in your extension's service files

thanks for your response. we're developing our webstore over SC 2019.1 and extending it using our own extensions (SCEM 2019.1). we want to use SS2.0 to perform CRUD operations on our custom records. do you think there's anyway we can directly make use of SS2.0 anywhere in our code? if not, then we'll be going with the way you suggested. the only thing that concerns us is that will the Suitelets break due to concurrency issues if a lot of people access it at the same time through the webstore?

Well my recommendation would be not use SS2.0, and use 1.0. I would also advise against using Suitelets in this manner; it's generally only advisable to use Suitelets for this if the Suitelet is going to be reused elsewhere within your instance.