Hi @RiiX,
you can definitely use a suction cup as @Frederic mentioned but finding the right pole size and suction cup to accommodate for it could be challenging. Moreover , the last thing you want is sand seeping though that suction gap and you risk losing the flag and cup altogether.
I went with the permanent solution where they bolted a small bracket to the OEM roof rails and u can just mount and quick release the flag pole whenever you want . They placed it in the way where it’s hidden and looks super flushed just like @JC_E mentioned. So far for me I didn’t experience and dents or issues with the bracket on the OEM roof rails.
feel free to ping me on WhatsApp and I’ll share more details on the garage. +971504801972
good luck and looking forward to seeing on the sand