If you mean the eight-bar B theme (chord of F major, melody notes C on the A string and F on the D string), it's part of the composition. Bert Weedon played it in a very similar way on his (slightly earlier) recording of
Apache.
You can hear the bit I mean at 0:51 and 1:34 on this Youtube video:
http://www.youtube.com/watch?v=rrEgYNOr-qcBert's version has a different arrangement - without the Shadows' mid-song chorus in a staccato rhythm - but lasts only a few seconds less than Hank and Co's because it is taken at a markedly more sedate tempo (not that the Shadows version is a rocker). The Shads, though, use the B theme three times, and it is on the third time that for the second set of four bars, Hank plays an
unmuted triad of the F chord, all on the sixth string (as far as I can tell): F (1st fret) - A - C - F (thirteenth fret). This part
may well be Hank's own invention. I'd probably put a quid on that.
It has also been said that Hank's intro and outro part was an on-the-spot invention. And to some extent, it was. But the same basic idea is certainly present on the Bert Weedon version, played an octave lower and with a more muted (in both senses) sense of feeling...
JN