At the moment there's no straightforward way to hide the InformationTip and keep the AditionalContent but there are two possible workarounds:
- edit the default RadDiagram and ItemInformationAdorner templates.
- find the information tip presenter in code-behind and set its visibility to collapsed
I've attached a sample project showing both approaches so could you please examine it and if you have further questions feel free to ask.
the Telerik team