DDEExecute OriginId, "run.section(FileName.OGS,SectionName);" 'run section of script file

A second option would be to place the script in a text label button on the default Origin.OTW worksheet template and then trigger the script to execute on Window Create. To create a text label button click the New Worksheet button to create a blank worksheet and then use the Text tool ( T ) on the Tools toolbar to place a text object on the newly created worksheet. Right-click on the text object, select Label Control, uncheck the Visible checkbox (if you want it to be invisible), select Window Create from the Script, Run After list box, and then enter the script

run.section(FileName.OGS,SectionName);

in the large white edit box. Finally, save the new worksheet with the text label button as a worksheet template named Origin.OTW. Whenever a new worksheet based on this template is created (like when Origin is launched) the script in the text label button will be executed. You will need to set up some sort of conditional mechanism to make the script not execute when you don't want it to (like when subsequently clicking the New Worksheet button).

No matter which method above you choose you will also need to create a text file in the Origin software folder named FileName.OGS (of course you can choose your own filename) containing the text

[SectionName]
// SectionName can be of your choosing as well
worksheet -s C1 0 C2 0; // select columns C1 through c2 in active worksheet
domenu 57637; // execute the Origin 5.0 Edit:Paste menu item

That should just about do it but there are a few other things you might also want to consider:
1. Menu id's can change from Origin version to Origin version so your script may not always be portable (the menu id for this menu item happens to be the same in Origin 6.0 so that should not be a problem here).
2. There is no way for users to acquire a given menu id in Origin 5.0 but in Origin 6.0 (and beyond) simply open the Script window and hold down the CTRL + SHIFT keys while selecting the desired menu item. The menu item does not get executed but the menu id of the selected menu item gets typed to the Script window.
3. Rather than Copy/Pasting data you might want to consider opening the Excel Workbook in Origin. Try the document -a LabTalk command. See the [OpenExcel] section of the text file File.OGS for example code. You can open the Workbook as either an Excel Workbook or as an Origin Worksheet.

This should get you started. Thanks for a hearty question.

-Gary