I don't know if this is even possible, but here is what I am trying to do.
I have the numbers 5 & 0 typed using the font "HaloHandletter" that have been converted to outlines. (This font has an open top on the "0".) I have stretched the top bar of the 5 and the top of the 0 toward an airplane icon. The goal is to create the look that they are formed by the airplane as contrails.
What I would like to do is have the gradient fade from lightest gray at the stroke edge nearest the airplane to black at the far point of the stroke - FOLLOWING THE SHAPE OF THE LINE. Below is an image of I'm working with.
Any suggestions, ideas, or assistance would be GREATLY appreciated!
What you can do is create a thick stroke with a gradient and use the letters as a mask on it.
For the gradient use either the gradient-on-a-stroke-option or use brushes (simulate the gradient with a blend for the brush)
i think you could make more satisfactory forms without using the typeface, in which case you could use open paths and run a gradient along them, or make an art brush that incorporates a gradient.
To create a stroke/nofill path following the shape of each letter without having to redraw, you may, working on a copy while locking the original (Smart Guides are your friends):
1) With the Scissors Tool cut the lettershape at both ends, there may be an Anchor Point there (Smart Guides will say anchor when you are there);
2) Change both new paths from fill to stroke only;
3) Make sure they have matching Anchor Points, you may need to insert one or more;
4) Object>Blend>Blend Options, set Spacing to Specified Steps = 1 and set Orientation to Align to Path;
5) Select both paths and Object>Blend>Make, then Object>Blend>Expand, then Object>Ungroup and delete the two paths.
This should give you a midline path.
You may then:
6) Increase the Stroke Weight so that it is wider than the (widest part of the) original lettershape.
You may then:
7) Apply the gradient along the stroke as already suggested by Monika, Doug, and Mike, or create an Artbrush based upon a blend and apply that to the midline path; this may be described further if you need it.
Finally, you may then:
8) Unlock the original lettershape and bring it to the top of the stacking order, then select both original lettershape and midline path and Object>Clipping Mask>Make, to mask as suggested by Monika.