You can convert your excel file to a script file, and then run it in autocad.
Script files are basically compiled autocad commands in written in Notepad. Simply copy and paste your coordinates to a notepad file (make sure the coords are space delimitted). Preceed your coordinates with the pline command, and then save the notepad file in a logical location. Then go to your autocad file, use the tools menu and select "Run Script...," and select the file you created. Script files are a bit tricky to run if you aren't careful where you place spaces. You also cannot use aliases or transparent commands in script files. It helps to practice on a few short plines, and see the results before you deal with a large group of coords.