If the total H2S removal rate required is a fairly low, adsorption is another options. SulfaTreat makes one such product. This is low capital, high opex option, so it only works economically when you have a low flow rate or low concentration.
One other option would be to use a pump that has suction lift, such as a progressive cavity or twin screw. I'm not sure how the price compares with Roth, but they're used in the oilfield rather frequently. Since it appears you already have a charge pump, this isn't likely to be your best...
I'm really surprised your company is so opposed to using a horizontal vessel for 3-phase separation. I use horizontal vessels for 3-phase gas, crude, oil seperation all the time for several different clients. If you are metering the products out of the vessel before additional separation, this...
