When I set up mechanical shifting + hydraulic brakes entering the head tube via the head set dust cover, I ended up with grease all over the hoses and cable housing, and I figured that'd help with cable rub for a while at least
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I only really feel some slight resistance when the handlebars are turned a lot, which I'd never do on rides.
I don't think foam would fit in the head tube of the Spcycle G056, at least not with 2x hoses + 2x mechanical shift housing. But some electrical tape on the steerer might work well.