In that case this is the best piece of advice I can give you. If you want to beat a grappler, you need to learn to grapple. Simple. BJJers train in a different way, with a different mindset and with different goals to most Aikidoka. The result is in a true application they are likely to have more functional tools availible to them. Or it may be better to say their tools have become more functionalised.
This is the only sensible advice. I too had the same question many years ago and so got into Jujutsu, Kungfu, Judo etc. And. at the end of the day, my Aikido is far better than it otherwise would have been. From my experience, if you did try to poke a BJJ guy in the eye or throat, it would just piss him off and make your situation that much worse. Best just get out of the way, seriously.