Is this for a connector or some very custom application? Typically a connector datasheet will tell you how to make the cutouts - often, a connector's pins would go through a round pad even when they are not round unless the expectation was to only utilize the solder side layer. Something to keep in mind - not sure if either work for your application.
As in my first suggestion, if you wanted to keep a non-round shape but maintain electrical (and thermal) continuity between top and bottom layers you can use vias to connect the top and bottom layers. There are a few factors to consider to make the right choice. It is a best practice to avoid putting a via into a solder pad because it can wick solder away from the component - so usually people put them in the copper plane of the pad but under soldermask. If your images the top and bottom pads do not look very big so you would have to decide to enlarge the pads to make space for this. Alternatively, rather than building it into the library you can use one or more vias on the board itself once you identify where you have board space.
Here is picture I found online of what I mean - in this case someone is using vias around a landing pad for a screw hole but the idea is the same for your slot. Picture is example only and I found it I did not make it.
Generally, 100mA is not very much current and one or more vias can certainly handle that for most applications. For virtually any current all you must do is determine the correct size and number of vias to handle your current load. I recommend Saturn PCB Toolkit (http://www.saturnpcb.com/pcb_toolkit.htm) to help you determine the best size for you. It depends on the copper weight of your board, the temperature environment you want, and any preference for either the size of the via(s) or the number. For example, because 100mA is so low, even a 10 mil via could handle the current but it might get too hot for your use case so then you could use 2 or more vias for added thermal reasons. Or change to a larger size via.
My only suggestion would be to contact your board house to find out the copper weight of via plating - even if your board is "2oz copper" the plating inside the via may be less. For example, a board house I have used in the past will use 0.787 mil plating for vias by default even on a 2oz board, which is closer to only 1/2 oz and affects the ratings.