You can use the OEM bar weights in renthal bars, I have done on mine, but it requires a bit of DIY. You need to use an expending rawl plug, I think it was M6 in size but I can't remember, they're used for masonry I think and can be bought in B&Q for a few £. You also need a couple of long bolts about 100mm to fit through the bar end and still have enough thread to expand the rawl plug, I also picked these up at B&Q and went for a rounded head which didn't quite fit in the recess of the OEM weight like the original bolts but still looked fine.
When you put the bars on and come to the final stages of grips and bar end weights, make sure the grips are slightly past the ends of the Renthals so about 1-2mm overlapping the end as the recessed part of the OEM weight doesn't quite fit inside the renthals and looks weird unless the grips are there to cover the overlap. Before putting the grips on, offer up the bar end weight to the bar and you will see the approximate overlap needed before you install the grips.
To install the OEM weights, put the rawl plug and weight together and the bolt through them then tighten the bolt up enough that when you insert the rawl plug into the renthal there is a bit of resistance. This makes it a lot easier to tighten. Then, when you're happy tighten the bolt up as hard as you can, you can also spin the weight to tighten it further. They may have a tiny but of movement if you try to very hard spin them the other way after installing, but as long as you keep an eye on them they should be fine mine have been for about 2500 miles now. I wanted to use the OEM because I like that they have some weight to them unlike the old Renthal bar weights I bought for my GS500 a few years ago that were garbage anodised crap that weighed nothing. Hope this helps, there's also a video on youtube of this idea somewhere if you need further info, type in delboys garage bar end weights and it should probably come up. Thats where I got the idea
I have the 789 I think it is, or "streetfighter" bar which I love but I don't think the fairing allows them to be fitted as they are too wide and the master cylinder or something fowls the fairing which I no longer have on my bike.