Posting my solution here so that it can help others out. The trick is to drag the remaining fields (BU, etc. in my picture in original post) to the area in Marks in the blank white space. Now it is possible to add reference lines (under Analytics) and choose one of these measures (BU, etc.) to display as a reference line on a per cell level basis, which accomplishes exactly what I was asking for.
I did not get this point how to plot multiple lines by using 5 or more measures on the same axis. Can you please share the sample workbook. So that I can understand easily how to achieve it.
The secret is to leverage [Measure Values] and [Measure Names].
If you look at the image above, you'll see Rahul has placed his date on Columns and [Measure Values] on Rows.
Placing [Measure Values] there causes two things to happen:
1) [Measure Names] appears in the Marks card as Detail and it appears in Filters, too!
2) A list of all measures appears in a box under the Marks card. It might look something like this:
Chances are you don't need ALL those Measures plotted-- but don't fret: just edit the list of Measure Names so they include only the measures you want to see. But how?? I prefer editing Measure Names in Filters (I just find it faster), or you can just drag the Measure Values you don't want out of the Measure Values list. It's up to you.
Make sure you check that they are being calculated correctly (generally they should all be the same-- like AVG).
Last but not least, change your Detail - Measure Names into Color - Measure Names. This will give each line a unique look.
Good luck & happy vizzing!