While ubiquitous data analytics is a promising approach, analyzing spreadsheets data on tablets is a tedious task due to the limited display size and touch vocabulary. In this paper, we present the design and evaluation of novel interaction techniques relying on the combination of a tablet, holding the data, and a smartphone, used as a mediator between the user and the tablet. To this end, we propose to use stacking gestures, i.e. laying one edge of a smartphone on the tablet screen. Stacking is a cheap, easy to implement and effective way of employing always-available smartphones to improve data analysis on tablets, by augmenting the input vocabulary and extending the display surface. We first explore stacking gestures to delimitate the possible interaction vocabulary and present the manufacturing of a conductive smartphone case. Then, we propose novel stacking-based techniques to perform spreadsheet data analysis, i.e. pivot table creation and manipulation. We evaluate our stacking techniques against touch interaction as provided by current mobile spreadsheet apps. Our studies reveal that some of our interaction techniques perform 30% faster than touch for creating pivot tables.