Something I originally came up with for GTA V. Just thought I'd convert it to GTA IV for old times' sake.

Installation:

1: Install this mod:
http://www.gamemodding.net/en/gta-iv/gta-iv-helicopters/23765-goodyear-blimp.html

2: Using OpenIV, access "C:\Program Files (x86)\Rockstar Games\Grand Theft Auto IV\pc\models\cdimages\vehicles.img" and replace the "tourmav.wtd" file with the one provided.
N.B. You will need to use Edit mode for this.