I don't believe there is, but even if there were, I don't think it would be the best way to proceed.
If you want to do advanced pre-processing then I think your best bet is to do so during a build process, by creating a front-end project as is commonly done when using the later version of the AEM Maven Archetype. Here are some advantages:
This is the direction that the AEM community is going, so you're more likely to be in line with best practices
The documentation around npm, webpack, node, etc. is much vaster than the documentation on AEM compilers
You will decouple your pre-processing from AEM, meaning that your website CSS can't be broken by a future AEM release
You have complete control over every aspect of your build for LESS, JS, resources, etc.