MrKrako :
There's not even much models of the 4GB version, so i highly doubt you will find one that only takes 1 slot. But, why do you want a gtx 750 ti with 4gb? It barely uses 2GB ram, so 4GB of ram would be a waste. Go for the 2GB version or go for a GTX950 and forget about the 4GB version.
I started of by looking at single slot 750 ti's 2GB and then I accidentally saw a 4GB version and it didn't cost that much more than the 2GB version but I didn't know that they are bad.
I can't get anything above 750 because my PSU will fry itself and I don't want to put money into my current PC as I will be trying to build a new one soon and I just want to save up money for that one.