Unfortunately, Adobe only stores dimensions (props, eVars, lists, etc) as text... even the "numeric" designation you mentioned doesn't change how the values are stored, it really only opens up options for tracking.
For example, when an eVar is set, and the value persists, you don't necessarily know what the previous value is. However, if you need to track an incremental number (to be used a dimension breakdown within your reports), numeric allows you to do something like:
s.eVarX = "+1";
This will mean on the first instance of eVarX, the value will be "1", the second time, the value will be "2"... but the values are still stored as a string.
So you can track currency in an eVar, but it will always be stored as text. There is no way to change that.
That said, if you need to track the currency into an eVar (and have it match the converted currency), I think your only option is to set up a VISTA rule with the Adobe Engineering team.. this will come at a cost, since you need to work with the engineers... but they should be able to create a rule to pass the revenue or currency based event into a dimension for you... I can't see any other way to do this.. Processing Rules don't have access to the purchase revenue, and they don't allow for setting a dimension based on an event (on top of that, there is no guarantee that the conversion has even taken place when Processing Rules are run, it very well might be done in the next step - it probably is after this anyway, since if the value was being set by context variable, processing rules would be used to set it to the event... conversion would have to take place after this).
If you had CJA, you could make a dimension from an event, or an event from a dimension.... but nothing like that exists in Adobe Analytics... sorry.
