Just get a bigger hammer ...
But, seriously, if it doesn't fit then it just doesn't fit. So far I've used Apple, JVC, Sony, and Bose headphones or earbuds and all have fit. Some go in a bit easier than others, perhaps, but the difference is small.
Not familiar with InEar brand, but what I think I'd do is do a visual comparison of their 'standard' 3.5mm mini jack plug and a few others. Their plug may just be mechanically different from most others.