@Andrew Duncan, if you look at several of the suggestions made recently on this thread, you'll find a common theme - try to keep some pressing volume while incorporating the 40 kg to the extent you can.
The other approach, while might or might not work for you, is switch gears entirely, going to very low volume with the 40 kg and adding volume from there. I have had some success with this in the past; what I did was take a bell I could press for only a single and take a GTG approach to it. I started with one single, once a day, rest days as needed; then one single two or three times per day, rest days as needed. When I got to the point where I could consistently do several singles throughout the course of a day, I took a day off then tried a double the next day, and got it, but just barely. So it was back to GTG, trying to build up to as many singles as I could to increase my pressing volume but without burnout.
If this approach goes well, then what happens is eventually you can start to GTG with doubles some of the time. Another approach, rather than try doubles, is to play with the timing by doing two or more singles on only a few minutes rest and GTG'ing with _that_ approach, e.g., in the morning you press x 1, wait 5 minutes, press x 1 again, and then you're off for at least 30 minutes and up to several hours.
The downside of this approach is its lack of volume - if it doesn't work out for you, you'll simply go backwards and find even singles with the heavier weight start to become more difficult and, if that's the case, it's not a good approach for you. But, if your schedule allows GTG, it might be worth a try.
A further word about GTG - some people talking about doing sets on the hour throughout the day but that has never worked well for me. I find a maximum of about 5 sessions per day suits me best, e.g., morning, mid-morning, noon, mid-afternoon, and before dinner. It's one thing to be doing 5 pullups all day long when you can do 10, but quite another, IMHO, when you are pressing a weight that's your current 1RM.
Maybe this is worth writing up in a little more detail ...
-S-