How to increase switching supply input range

I am using readymade switcing supplies in Industrial project. Normally all supplies have input voltage range 100V to 240V. In our industrial envoirenment sometimes voltage goes upto 260V that may remain even for few seconds. The result is damage of supply. How to increase upside input range without opening supply. solution should be simple as multiuple modules are used in one site.(may be 100 or more)

Maybe a buck transformer would be a good solution as long as the problem is always voltage that is too high - and as long as the supply can tolerate a lower voltage.

Thanks stevez.
I have already ordered for that but have less space in product casing to place the transfer. So looking for any electronic protection as it consumes less space.

A lot of switching power supplies have a switch (Or jumper dongle) that changes the input rectifier from a fullwave (240VAC) to a voltage doubler (120VAC)..... I assume yours has no such switch, however, you can check if it has a voltage doubling rectifier on the input. If it does, it will have 2 large input caps connected in series which are easy to spot. If so, you can modify it for fullwave input. This would raise the minimum input voltage and the max by about 2X. You would have to open the supply though.

Normally these sort of power suplies are rated to 260V or more and will stand even higher voltages for short periods of time. The big smoothing capacitors are probably rated for 400V, and the same for all the other componants, it'll probably stand surges of at least 280V for a couple of seconds and the on board suppressers can probably clamp spikes of 2000V or more.