Plot on axis a different range than that one used for graph

I would recommend a variation of this "vertical category axis" technique: http://peltiertech.com/Excel/Charts/Y_CategoryAxis.html

The basic idea would be:
1) Create a second series. The X-values for this series should be locations along the x axis where you want the "trip number" labels to appear. The y-values should be 0, if you want these labels along the x axis, or some other suitable value, depending on where you would like the labels to show up. Include a column with the desired trip number for each point
2) Add this series to the scatter chart.
3) Using Rob Bovey's XY Chart labeler add-in (appspro.com), label this new series with the desired trip labels.
4) Format the 2nd series as desired (you could even format as no marker no line if you want it to be invisible except for the labels).