In recent versions of FreeCAD you can find graphical tool called Loft. It helps to make an extrude based on two or more sketches.
Create a sketch with H-like shape, it will be our conrod cross-section.
Next create two copies by selecting the sketch and using menu Edit-Duplicate Selection. You should have 3 sketches: Sketch, Sketch001 and Sketch002.
Translate the Sketch001 (~80 mm) and he Sketch002 (~100 mm) along Z-axis. You have to change Placement-Position in Property view tree (the sketch should be selected during operation).
The sketches should be different, so change some dimensions.
Now you can open the Part workbench, and select menu Part-Loft... Then move all sketches in the Task view to the Loft field. Check also Create solid option.
If effect isn't good, you can re-edit sketches.
Download RAW Video.
FreeCAD 0.12 5088 SVN