No. It is not possible with the DGN2200, because it doesn't even have bridge mode, let a lone half-bridge mode which you're looking for.
You can always go and buy a D-Link DSL-2500U ADSL modem, which goes for less than R200 (incl VAT) and it supports both bridge & half-bridge modes. You then connect your Netgear DGN2200 to the D-Link ADSL modem so that you can still have a WiFi Access Point for Internet

I'm actually not sure if it is even possible to do this with the DGN2200 since it doesn't have bridge mode. Hopefully someone on this forum can tell you whether this kind of setup is possible.
With the D-Link you'll have to enable the 'Bridge PPPoE Frames Between WAN and Local Ports' setting of the PPPoE connection that will be used as your default Internet connection, which enables half-bridge mode.
You should now be able to dial a PPPoE connection from that PC where you want to use another ISP account.
Please just take note that you will be sharing the ADSL line's capacity, so if you're using 2x 4Mbps uncapped accounts on a single 4Mbps ADSL line, then you'll still only be limited to a total of 4Mbps download, and not 8Mbps.