Hi Tina
This is not an uncommon request and it may require some work with the customer to get to the right solution.
You mentioned that your data has higher dimensionality, consolidations differ from the working days ratio, rules cannot be used due to multiple spreading options, and users find processes impractical or complicated. Realistically, "complicated" tasks, like having multiple spreading options available where working days are one option, require some effort from the user.
In my projects, I always emphasize to customers that functionality, administration, and performance are interconnected. High functionality typically comes at the expense of administration and/or performance, while low administration comes at the expense of functionality and/or performance.
As others have already stated, if rules are not an option, then TI processes are the only viable solution. You will need to collaborate with the customer to find the best possible compromise given the requirements and technical possibilities. It should be possible to get the customer to decide on which solution is the best for them once they know the pros and cons of each solution. As always, informed decisions are always the best.