If there is no tag for connecting to then I would either look for another bolt to fix to with ring tag or even put an earth clamp around one of the legs (nice and tight of course)
Cross bond H+C for good measure also.
If the supply pipes are in copper which are already supplementary bonded and the bath not in contact with any other ecp (such as a metallic building structure) I would question the need to bond it anyway. Bit in here at the bottom: http://www.iee.org/Publish/WireRegs/EarthingPlasticPipes.pdf
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