Why couldn't you? If the SDK has an object, the ruby and the python bindings have it too (very rare exceptions aside)
SDK Documentation: MeterCustom Class Reference
Ruby example of API: OpenStudio-Resources: meters.rb#L68-L88
Python works EXACTLY the same, syntax aside.
In [1]: import openstudio
In [2]: m = openstudio.model.exampleModel()
In [3]: meter = openstudio.model.MeterCustom(m)
In [4]: meter.setFuelType("Electricity")
Out[4]: True
In [5]: for l in m.getLightss():
...: meter.addKeyVarGroup(l.nameString(), "Lights Electricity Energy")
In [6]: for e in m.getElectricEquipments():
...: meter.addKeyVarGroup(e.nameString(), "Lights Electricity Energy")
In [7]: print(meter)
OS:Meter:Custom,
{22211bf0-8e18-4956-9e3c-3038f8e7723e}, !- Handle
Meter Custom 1, !- Name
Electricity, !- Fuel Type
Lights 1, !- Key Name 1
Lights Electricity Energy, !- Output Variable or Meter Name 1
Printer, !- Key Name 2
Lights Electricity Energy, !- Output Variable or Meter Name 2
Electric Equipment 1, !- Key Name 3
Lights Electricity Energy; !- Output Variable or Meter Name 3