Galerkin-Bubnov Integral Boundary Element Method (GB-lBEM) is used to model transient phenomena on thin wire structures directly in the time domain. One of the most prominent limitations of the method is the inability to deal with the structures above finally conducting half plane, due to the high computational inefficiency when ground losses are accounted for in the numerical model. In this paper, this problem is tackled via various modifications, in order to optimize GB-IBEM with respect to the computational speed. These optimizations of the original method result in several orders of magnitude improvement in the overall calculation time, allowing GB-IBEM to be used with geometries above lossy ground.