Instead of creating a pop-up topic, you can use a HyperAlert or HyperAlertTitle PI marker, and provide pop-up content in the text of the marker itself.
You designate a hotspot the same way as for other hypertext links; see §17.8.4.1 Using HyperPopup and HyperJump PI markers. Type the marker text in the PI marker as a reference string consisting of the base file name, followed by Alert, followed by a number, starting with 0001 in each file. For example:
chap1.hlp Alert 0012
The pop-up text appears in the default format; you cannot specify a different format.