Thank you for the question. ToolTip does not support the described functionality. However, you can use a ScreenTip in this case. It offers extended formatting capabilities compared to ToolTip. Please, consider the following code:
sender, Telerik.WinControls.ScreenTipNeededEventArgs e)
AppointmentElement appointmentElement = e.Item
RadOffice2007ScreenTipElement screenTip =
"This is a ScreenTip"
appointmentElement.ScreenTip = screenTip;
Do not hesitate to contact me again if you have any other questions.
the Telerik team