If a big part of the pricing structure of Costco gas is to drive customers to the store after filling up, then it probably doesn't make much sense for the pumps to be too far from the warehouse.
While my Ikea suggestion was a tongue in cheek suggestion, the reality is there are not a lot of options nearer to that Costco and if there were any, the cost of the real estate might not justify the expense for a bunch of likely money losing gas pumps that are just to draw people in.
Given most Costco customers probably come from a 10 mile radius and you can only use the pumps if you are a Costco member, anyone driving to that general area is likely to visit Costco even if the pumps are a mile or two away at that point. I would imagine a big portion of their customers arrive via I-295 (or could do JTB to I-295) so exiting Ikea is not a big deal and Gate Parkway goes straight to Costco from there. Importantly, a 1,000 extra visitors to Ikea's property may be a drop in the bucket for that property.
Looking at an aerial, the very best option would be to buy out the Daily's station in front. This not only would give them a ready made setup for the pumps but might create an opportunity to redesign their entry point from Gate Parkway which is desperately needed. If they did build out a gas facility on the Costco property it could put the Daily's in a very bad situation so maybe Daily's would then rather sell vs. fail to compete. Interestingly, there is also a second Daily's only 1,500 feet away to the south on the other side of the JTA interchange thus the stations may be cannibalizing each other's business and it may not hurt Daily's at all to give one up.
It really comes down to what options do they really have to locate a somewhat large pump facility that will generate a 1,000 visits a day or more.