Liquid can load and use many VSTs (audio plug-ins, many freely available) so there is no shortage of audio filters and effects. What you generally have with consumer camcorder microphones is a fairly limited range with a pronounced drop off at the low end. Try just adding one of the built-in equalizers (I suggest the standard Real Time Equalizer filter; it's the easiest one to use if your not familiar with sound processing). Start with the Vocal preset. That alone might be close enough to get what you want. If not, try increasing the mid-range and the low range (from 250hz up) and see if that fills in the sound better. If not then you'll have to do a bit of searching on the web for a VST to help.

Good luck.