In this paper, we propose a novel approach that calculates all the possible applications of synthesis rules, for well-formed free-choice Petri nets , in a speedy way to enable an interactive editing system. The proposed approach uses a so-called incremental synthesis structure, which can be used to extract all the synthesis rules, corresponding to a given net. Furthermore, this structure is updated incrementally, i.e. after usage of a synthesis rule, to obtain the incremental synthesis structure of the newly synthesized net. We prove that the proposed approach is correct and complete in order to synthesize any well-formed free-choice Petri net, starting with an initial well-formed atomic net and the corresponding incremental synthesis structure. A variant of the proposed approach has been implemented that allows interactive modeling (discovery) of sound business processes (from event logs). Experimental results show that the proposed approach is fast, and outperforms the baseline, and hence is well-suited for enabling interactive synthesis of very large nets.