Application-specific instruction set processors (ASIPs) extend the instruction set of a general purpose processor by dedicated custom instructions (CIs). In the last decade, reconfigurable processors advanced this concept towards runtime reconfiguration to increase the efficiency and adaptivity. Compiler support for automatic identification and implementation of ASIP CIs exists commercially and on research platforms, but these compilers do not support CIs with memory accesses, as ASIP CIs typically work on register file data. While being acceptable for ASIPs, this imposes a limitation for reconfigurable processors as they achieve their performance by exploiting data-level parallelism. Consequently, we propose a novel approach to CI identification for runtime reconfigurable processors with support for memory operations in contrast to previous works that explicitly exclude them. Our algorithm extracts memory access patterns which allows us to abstract from single memory operations and merge accesses to optimally utilize the available memory bandwidth. We implemented our algorithm in a state-of-the-art compiler framework.The largest CI identified in our benchmarks consists of 2071 nodes (average 999 nodes), and a single generated CI can cover a whole computational kernel (up to 99%).