Jiggery-Tackery

I'm practicing making joints.

I built a simple jig to hold two pieces of tubing parallel and about
6" apart and have notched and placed a third piece of tubing,
connecting the two parallel pieces at 60*

To minimize warpage from the heat (I'm using gas) I know I should tack
one side of the joint, then the other, then repeat at 90*

So how do I get to the other side of the joint (for the second tack)
if it's lying flat against the board? Certainly the folks building a
fuselage don't take it out of the jig after doing only one of the four
tacks per joint - Mike