ipympl for matplotlib not created through pyplot

Is it possible to use ipympl starting from an arbitrary matplotlib figure? If yes, an example would be helpful. Thanks!

Use Case: I would like to use ipympl for SageMath plots. The later do have a method to
convert them to matplotlib figure. However the figure has not been created with the usual
pyplot workflow, and does not have a canvas setup.

In a jupyter notebook with the SageMath kernel (e.g. using the binder link from https://github.com/sagemath/sage-binder-env/ after installing ipympl with `sage -pip install ipyml`)
```
%matplotlib widget
p = plot(sin(x))
fig = p.matplotlib();
type(fig.canvas)

```

It could well be that SageMath is producing weird matplotlib figures though.

cc: @zerline

No project files or tests are named. Start by reproducing the Jupyter notebook snippet with the SageMath-produced matplotlib figure and inspect whether ipympl can provide a canvas for it; done means establishing whether this workflow works and documenting a minimal example or the limitation.

Written by the indexing model from the issue text.