Sadly seems like it's way too small. Pioneer 10 is ~2.9m long [1] and 2.0e7 km from Earth [2]. JWST is just 1.5e6 km from Earth, so that doesn't make much of a difference. Doing the trig, you get the arc-width of P10 is 2atan(w/2d) = 2atan(2.9m/4.0e7km) = 7.33e-14 rad. JWST has a resolution of 0.1 arcsecond = 4.8e-7 rad [3].

So we're off by "just" a factor of 10,000,000 on resolution :-(

It's too bad, that would be so cool.

[1] https://www.space.com/17651-pioneer-10.html#:~:text=This%20s.... [2] https://theskylive.com/how-far-is-pioneer10#:~:text=The%20di.... [3] https://www.spaceanswers.com/astronomy/ten-reasons-why-nasas...

My guess is that it is too small, but the RTG is warm.... :).