Did you know you can add an SEI worksheet to open from within X3?
There are two ways to accommodate this functionality, either by embedding it into a landing/home page or adding it within the menu modules as a menu item.
These two knowledge base articles contain all the necessary steps:
KB 79475 SEI Can I get SEI to open from within X3?
This article contains steps for how to determine the URL to copy from SEI, create a Menu Item within Sage X3 which points to a URL, and how to insert the Menu Item (Gadget) into a landing page.
KB 87887 How do I add my own module block to an existing menu group?
This article contains steps for adding a Menu Item (Gadget) to a sub-module and associating that sub-module to the Purchasing module. Also, in the "Additional Information" section, steps detail how to create a new custom Module to which you may associate your custom sub-module and custom Menu items.