The Burgers are pretty low slung already (in terms of ground clearance), so your options there (if there are any) are pretty limited. Even if you could you would have to ride pretty sedately in the twisties which pretty much negates the reason for upgunning (I think). These sorts of modifications may also impact on insurance (significant modification) and Suzuki would likely walk away in any product liability issues - should they arise.
I think your best option is the customised seat (and probably tailored to you) to reduce cushion height to the minimum acceptable for comfort.
This in combination with extra thick soled riding boots might do the trick.
Also, bypass the side stand interlock so that you have the option of kicking it down while stopped in traffic - could be useful in your sit.
I really don't think that the AN650 could be lowered much. The seat would probably require a modified seat pan to lower it as well. That said, there is always some talented individual out there who might prove me wrong, but I do think you would end up with compromised handling and ride characteristics, and possibly some strange ergonomics.
Better off buying a machine that fits you, and tweaking performance if you wish later on. With the 400, a Malossi variator and a performance exhaust are possible enhancements. Add some Fehling chrome trim, and you've got a scoot anyone would be proud to show off. And all that can be done a step at a time as budget allows, whereas you'd need to do the 650 mods before you'd even feel comfortable riding it.
One interesting thought. A tow-pac "minitrike" kit would allow a fairly short person to ride a 650 - since the extra wheels would hold it upright anyway. But that is a $2000 add-on, and it would definitely change the handling characteristics of the machine.
My wife is a shorty, too. (5'2") When she comes to a stop, she slides way forward on the seat, but still can't flatfoot. It doesn't seem to bother her, though. With the Clearview XXL, she looks like a little kid when she rides it, but she does okay.
I took my 650 to a local auto-upholster. He shaved the padding and put a gel-pad in the place and re-covered.
The seat was lowered by about an inch and a half without loosing comfort. Cost was $290 including parts (gel-pad).
IMHO, after observing while he was working on my seat, I think it might have worked well for the purpose simply by shaving the sides of the seat padding making it narrower.
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