🚀 go-pugleaf

You should create a text frame using kCreateMultiColumnItemCmdBoss instead of IPathUtils::CreateRectangleSpline. Using this command automatically associates a new text story with the multicolumn item.
(See SDKLayoutHelper::CreateTextFrame).

Then, you need to navigate over to the kTextStoryBoss (ITextModel) that is associated with your new multicolumn item, then call ITextModelCmds::InsertCmd to create the insert command, and then process it. (See SnpTextModelHelper::InsertText)

You might find a lot of other tips if you look at the slides for these online plugin development training sessions:
* Session 11: Text Model
* Session 12: Text Layout

You can access these from <http://partners.adobe.com/asn/indesign/sdk.jsp>. (ASN WebLogin required to access SDK contents)