Is there a work around to a presta valve not engaging a tire inflater pin? I believe that either the schrader adapter I'm using is too long or the pin for the presta core isn't long enough for me to be able to use an air compressor. It works fine with a floor pump since a pin doesn't need to be engaged for air to come out. But in my situation of trying to seat a new tire, a pump won't work. I've been searches to see if there are other valve stem adapters that allow this.
You're using the wrong inflator valve on your compressor. 

You're likely using this type of inflator valve (aka chuck). It requires the inner pin of the schrader valve of the tire to depress the inner pin of the chuck for the chuck to release air:



Instead you need one of these types of inflator valves which have a manually activated release mechanism (the lever or trigger). The advantage of these types is that they often have a built-in pressure gauge, such as the model on the right. The gauges are not very accurate but are sufficient for eyeballing pressure.



If the valve on your compressor is not replaceable (because it's not your compressor, for example) then you can fill up a portable air tank with the compressor (these tanks have schrader valves) and then hook up your manual-style shrader valve inflator to them. This is also a way to use a tiny little 12VDC electric tire inflator (such as in emergency kits) to build up enough pressure and air reserves to set tubeless tires. It might take an hour to build up 5 gallons at 135psi (and you might burn out a tiny compressor, so you'd take it in chunks) but 
you'd have enough air to certainly set even a car tire.

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Note that this tank has the type of schrader valve outlet that you don't want, but you can easily swap it out.