How to Get Gnuplot to Read Input File with Hex Data

Question

I'm collecting data from a CAN bus viewer that saves it as a text file in a fixed column format, like this:

  4681)     24123.0  Rx         0488  8  79 00 DF 58 66 00 FF 00

I'd like to have gnuplot create a plot using column 2 for 'x' and the sum of columns 10 and 11 as the 'y' value, where column 10 is the LSB and column 11 is the MSB (so it needs to be multiplied by 256 first). Both columns 10 and 11 are in hexadecimal. The documentation I've read implies that a sprintf format can be used, but I'm not having any luck getting the correct syntax.