So I'll throw out an idea that isn't fully formed, and see whether it has any merit based on the experience of others. My previous H36, a newer sister to the H356 line, had the same Selden in-mast furling system. But interestingly it also had a mast slot to port of the large slot where the in-mast sail furled. I never paid much attention to it, but I vaguely recall reading somewhere that the slot was meant to take a mainsail with traditional slugs. Here's a cross section from overhead from the Selden manual with the track circled in red:
View attachment 212616
If that is indeed the purpose of the red circled area, could one remove the furling main used for cruising, and replace with a standard slugged main when you want to race? The more accessories you want to add (e.g. stack pack, etc.) will make such a conversion a lot more effort, but if you only race occasionally and want a slugged main perhaps you forego those other mods to make the temporary conversion quick and easy?