The aim of our work is to provide a mechanism to deal with soft real-time aperiodic traffic on top of a fixed priority scheduler, without any kind of modification on it. We want to reduce as most as possible the time and implementation complexities of this mechanism. Moreover, the overhead of the framework has to be completely integrated in the feasibility analysis process. We propose a naive but low cost slack time estimation algorithm and discuss the issue of its utilization at the user level. We validate our work by extensive simulations and illustrate its utility by an implementation on top of the Real-Time Specification for Java (RTSJ).