I got conflicting answer on where this laptop has MXM gpu in there. There is a Swedish site that is selling MXM gpu for it but Yahoo answer says no. Although I would guess it is not MXM. Open it and check if the gpu is removable MXM. If it is, then ask MSI if their bios allow the recognition of additional gpu and which gpu it will recognise. Buy the MXM gpu with the matching version and type of slot and put it in.
Otherwise You have two option:
1. vidock if you have expresscard slot or 2. you can open the computer and use the mini pcie connector, connect mini pcie connector to pcie x16 converter and a desktop psu for power. But I don't think you want to do either because you have no mobility at all (external monitor and power for external gpu required). Either way, your graphics card will be very bottlenecked by the bandwidth which IMO is not worth it and is better to sell your current laptop and combined with the money you save and spend it on a desktop gaming build or a gaming laptop if you need mobile gaming.