Item On Any Line option in a formula?

My problem is I need to classify sales orders by product line, and the mix of various product skews on a given order determine that product line.  I can't go by the Class as indicated in the item record as we have products of the same Class that span different product lines.  For some orders I can go by certain fields in the Customer record, but for others I'm left with a not-so-straightforward means of classification.

In our account in a transaction search the option 'Item On Any Line' is available in the Criteria tab drop-down list, but not available in the list of fields when writing a formula, nor is it available in the Results tab (it is available in the Available Filters tab, which comes in great handy when used in a Search Form).