Programmable switches have been widely used to design network monitoring solutions that operate in the fast data-plane level, e.g., detecting heavy hitters, super-spreaders, computing flow size distributions and their entropy. Many existing works on networking monitoring assume switches deploy a single memory that is accessible by each processed packet. However, high-speed ASIC switches increasingly deploy multiple independent pipes, each equipped with its own independent memory that cannot be accessed by other pipes. In this work, we initiate the study of deploying existing heavy-hitter data-plane monitoring solutions on multi-pipe switches where packets of a "flow" may spread over multiple pipes, i.e., stored into distinct memories. We first quantify the accuracy degradation due to splitting a monitoring data structure across multiple pipes (e.g., up to 3000xworse flow-size estimation average error). We then present PipeCache, a system that adapts existing data-plane mechanisms to multi-pipe switches by carefully storing all the monitoring information of each traffic class into exactly one specific pipe (as opposed to replicate the information on multiple pipes). PipeCache relies on the idea of briefly storing monitoring information into a per-pipe cache and then piggybacking this information onto existing data packets to the correct pipe entirely at data-plane speed. We implement PipeCache on ASIC switches and we evaluate it using a real-world trace. We show that existing data-plane mechanisms achieves accuracy levels and memory requirements similar to single-pipe deployments when augmented with PipeCache (i.e., up to 16x lower memory requirements).