The Half-Way Trick
This is a nice workaround but it unfortunately only works on certain models of Handycam.
This method can work on both vertical and horizontal switch configurations - patience is the key to success. The trick is to move the switch to a point, about half-way in its travel. At a particular point, the internal infrared blocking filter is pulled clear of the CCD but the internal microswitch has not yet been pressed.
This makes the camera sensitive to infrared light, but it doesn't know it's in NightShot mode and therefore still allows full control of the exposure.
The only draw-back with this method is that the internal mechanism for shifting the filter can sometimes be seen in the corner of the screen, particularly while using zoom. Careful adjustment of the nightshot switch can prevent this.
Also, the button tends to suddenly spring back to on or off, so a small piece of insulating tape fixed over it should help. Alternatively, make a small rectangle of rubber by slicing down a pencil eraser (dark coloured if you can find it) and slide it in the path of the switch to prevent spring-back if you have a vertically moving switch.
This work-around allows you to use any infrared filter as if you had an original unmodified camera.
If you are unsure whether the half-way trick is working or not, you can perform the simple tests shown below before you choose your infrared filter.
The Infrared Remote Test
Film an infrared remote control that has an opaque window on the front.
Push the switch half-way and the window on the remote should become transparent. Notice that Nightshot Mode is still not engaged and full exposure control is available. Also, you may notice the image takes on a red tint.
The Cigarette Test
Film an ordinary lit cigarette.
Push the switch half-way and you should notice the tip of the cigarette glows much brighter than it did before and the white paper takes on a red tint. The tip glows brightly because burning substances emit strong infrared light (the sun is the biggest example of this).
If you can replicate either of the tests above, the half-way trick is working for you!