We used weak polyelectrolytes (polyallyl amine, PAH, and polyacrylic acid, PAA) to demonstrate that their complex formation can be controlled under out-of-equilibrium conditions. We hypothesized that a surface-bound polycation, poly-L-lysine (PLL), would increase the history dependence of the PEC as it mainly influences the process that relied on the positively charged polymer. The presence of PLL enhanced the continuous adsorption of either PAA, PAH or the complex PAH-PAA and, instead, supported rather than perturbed the assembly of the PEC. The role of the surface was further exploited for molecular information processing, which we demonstrate by transforming a temporary sparse input pH to a spiked output based on PEC.