Retail Promotion Best Practices for setup and activation

Hi all, we are running into an issue wherein we are exceeding article/store combinations for activation of a mass promotion within SAP ECC with IS-Retail. The scenario is this: We create one promotion that has ALL of our articles (~18,000) and for ALL stores (166) that would give the customer - everything a 20% off for a period of time. While trying to activate this said promotion in SAP (TC: WAK16), we are getting errors due to SAP "technical limits" of processing (~2.9 million entries). SAP is stating that we need to limit our promotion entries to around 500,000 entries (or certainly less than a million) per promotion combo of (Article X Site). What we are wondering is how other retailers have set up retail promotions storewide with all articles successfully? Multiple promotions (with either a subset of stores and/or articles) or other? Is there certain configuration that we are missing that allows this? We are not a large SAP customer (more midsize) - so certainly this was solved for larger retailers...but would like to know how this was solved. If this request needs to be moved to another forum, please advise! Much appreciated for any thoughts and advice on this.