With the KP_CurveTools plugin you can extrude objects (cubes) along multiple curves at once (figure A). The tool features several parameters to customize the extrusion (figure B) and has the option to create a new set of controls (figure C) for later animation of the extruded objects (subdivs, position along curve, thickness, etc.).

Figure A

Figure B

Figure C

The same tool has been used to create this wiry guy:

To download the XSI 6.01 Add-On click here: KP_CurveTools.xsiaddon
To download just the JScript plugin click here: KP_CurveTools.js