I'm sure this isn't what many will consider a solution and I'm not weighing in on this issue at all. I just ordered my strap (and Amazon's delivery date just updated from June 21st to Friday! :O) so I am not actually offering an opinion on whether or not the foam is problematic or anything.
But whenever I am doing stuff in VR for extended periods (I do a cardio circuit with weighted clothing) that I know will get me sweaty, I wear one of these awesome sweatbands: https://smile.amazon.com/gp/product/B00Q6HL0X2/ref=oh_aui_search_detailpage?ie=UTF8&psc=1
Which generally helps with comfort and may or may not assist with this issue. Just putting it out there!