Sorry to chime in since by no means am I an Brainstorm expert.
But could you not simply redo whatever your statistical test is in source space using all electrodes, without correcting for multiple comparisons?
From my understanding, that is one option as suggested here:
https://www.sciencedirect.com/science/article/pii/S1053811912009895?via%3Dihub
When an effect is significant at the sensor level with all the proper corrections for multiple comparisons and the hypothesis is about the existence of an effect rather than about a specific area being involved, it could be acceptable to only report the peaks of a statistical map at the source level without requiring correction for multiple comparisons over the whole brain.