Okay.

Personally, I would just get a new mouse, because you can definitely get a new ambidextrous wireless mouse with side buttons for a lot less than I'd consider the work involved with this being worth it to me.

If you really strongly want to do this, two possible routes:

• You don't actually need the PS/2 plug, just the chips and electrical connections. Dissassemble the PS/2 dongle and a PS/2 to USB adapter and rewire them into a smaller form factor that you're comfortable carrying around with your laptop.

• Rip out some or all of the internals of the mouse and replace them with internals from a newer, Bluetooth-compatible mouse that uses the same encoders that are encoding the ball's movements, assuming such a thing is out there. That won't give you the same mouse, but it'll give you something that has the same external feel. The shape will be the same, it'll click the same way, and it'll have the same rolling feel when moving.

Finally, a partial solution: it sounds like your concern with the dongle plus adapter is mostly that you don't want to carry more components with your laptop.

If you regularly carry other USB peripherals, you can just bundle them up with a USB hub and the dongle and then just have one box that you plug into your laptop. That might mitigate the issue of carrying the dongle, or might not. Depends on what it is that's problematic for you – a lot of parts or the bulk of extra components.

At one point in the past, I had an optical trackball with a translucent pink ball that I wanted to use in a dark room. The red LED was really disruptive, and while an opaque ball would have mitigated it a bit, it still would have shown around the edges. The fact that it went to sleep when being inactive and then woke up when moved, changing in brightness, made it annoying as hell. Those optical sensors can also see into the near-infrared, so I took a gamble and ripped out the red LED and put in an infrared LED. It mostly worked, except the sensitivity was reduced enough that when it was in sleep mode, any movement wasn't enough to reliably wake it up. I dug up the datasheet for the chip, found the pin that sent it into sleep mode, and wired it to the high voltage pin so that it never slept. That worked fine. All that being said, while it was satisfying to have it work, the only reason I was willing to to it was because I couldn't just buy an optical, off-the-shelf trackball at the time that didn't shine a red light all over. It simply would have made no financial sense to put the time and money into doing the modifications otherwise. In this situation, if there's an off-the-shelf product that does what you want, I'd probably drop the mouse off with Goodwill or similar if you don't want to toss it in the trash – maybe someone out there does want a mint condition PS/2 wireless mouse – and just buy the new mouse.