Here is a manual way. I used it to overlay a 45 degree line onto a regression plot but also works for your bubble plot.

First, make your bubble lot and then separately obtain your regression line. I assume you do not want the raw data so be sure to click off Show Points in the Bivariate Fit red triangle. Then in that regression line graph, rt-clk Edit:Copy Frame Contents, then click on the target graph (bubble plot) to make it active, and rt-clk Edit:Paste Frame Contents. That places your regression line (contents of the regression frame) onto the bubble plot frame. You need to have the Arrow active, not the select (cross) tool, when right clicking. Interesting that at least as of JMP10, the two graphs do not need to be the same size. If the x-axes are not the same, the line is still accurate but might not fill the space: if the target x-axis is longer (wider) than the regression line plot, the line only goes to its original x-width. I have not found a way to script this yet.