Plenty of straight guys I know have dildos to use on ladies.. or for ladies to use on them. If youre closeted you could just claim that's the reason.
Or you could hide it so they won't find it, I used to stash a lot of stuff in a teddy bear when I lived at home, the open seam was covered by it's clothes. I wouldn't go shoving foreign objects, that weren't purpose made for it, up there - they could have harmful plastics or varnish etc.
Actually this is a great advice. Get an accurate size dildo and hide it.
Or you could use your fingers, they're free and nobody suspects on it…