Let them know (email, phone) that it is their dropping of Beck/FOX ads that is the reason for no longer patronizing them.
Remember, one side's boycott doesn't have to "outrank" the other side's in terms of lost sales revenue, it is the combined total that resulted from the company's ever responding to the political controversy in the first place. Including the rest of this list (G-Z0 this is an awful lot of co.'s.
If it's easier just boycott everything General Electric. Then that includes a lot of co.'s as well.

# FreeCreditReport.com/Experian (added 8/24/09)
# GEICO
# General Mills (added 8/27/09)
# Healthy Choice (owned by CongAgra)
# Johnson & Johnson (added 8/24/09)
# KRAFT Foods (added 8/20/09) (read statement here)
# Lawyers.com (owned by LexisNexis)
# Lowe’s (added 8/24/09)
# Men’s Wearhouse
# NutriSystem (added 8/24/09)
# Procter & Gamble
# Progressive Insurance
# Radio Shack
# Re-Bath (added 8/17/09)
# Regions Financial Corporation (added 8/27/09)
# Roche

# Sanof-Aventis
# Sargento Cheese
# S.C. Johnson*
# Sprint (added 8/23/09)
# SAM (Store and Move) (added 8/27/09)
# State Farm Insurance
# Travelers Insurance (added 8/27/09)
# Travelocity
# UPS (added 8/23/09)**
# Verizon Wireless (added 8/21/09)
# Vonage (added 8/24/09)
# Walmart (added 8/17/09)

Many of those are misleading. Walmart along with many others aren't boycotting Beck or FOX, they simply said the hell with this and pulled their advertising off of all political talk shows on all the cable networks.