הלכך אותה ישיבה מעוטת אם תימצי לומר לא גרעה מטיול, אין כאן ברכה לבטלה שבלי הלקט שמז R. Zidakah from Roma ask R. Avigdor Cohen Zedek about the custom of people who have no Sukkah who were accustom to sit in the synagogue sukkah for a minute or two and say the bracha, whether this is a bracha l’betalah. He answer that the gemara is that one can walk, drink, learn torah and eat in the sukkah. Sitting for a minute is more than tiyul so there is no problem, although it would be best to say some torah. Can one rely on such logic in שעת הדחק?
There are many opinions as to what requires a "bracha" when in the Sukka. The many opinions are brought in brief in the Talmudic Encyclopedia (Hebrew edition volume 26). The opinion of the Rif and the Rambam is that upon each time one enters the Sukka whether to eat, drink or just to sit one makes the Bracha which requires less than what you quoted from the Shibolei Haleket in the name of the Geonim. רי"ף, סוכה פ"ד (כב א בדפי הרי"ף: כל שעה שנכנס לישב בה,' רמב"ם סוכה פ"ו הי"ב) However, this is not what is practiced by most people besides those who adhere to the custom of the Vilna Gaon (סי' תרל"ט) or the custom of some of the Yemenite Jews. (See commentary of Rav Yoseph Kapach zt"l to the above Ramabam. ) Most people follow the practice of making the bracha only when having a se'uda. The criteria of what constitutes a se'uda which requires a bracha, is dependent upon the custom you follow. May you have a healthy winter.