Can I put Netgear CG3000D-RG into Bridge mode

Short answer: No

I don't think you can. It doesn't seem to have any Firewall Options at all except for DMZ, which looks to work in Potluck mode. You have your standard Port Forward and Trigger, but that still keeps the traffic above layer 2. Even the manual looks to be made for customer's of ISP's and not general consumers. I have personally used this device and I found it's performance horrible. I think you will be much better off getting a stand alone modem.