Convertible top glass window fell out. How do I fix this?

I came out of work to my Boxster yesterday and the glass rear window had completely fallen off the top and was sitting on the engine cover.  

This top is aftermarket and not that old from the looks of it, so I would prefer to repair rather than replace the whole top. 
 

I know I need to glue it back in, but how is the problem.  3M window weld is probably the solution, or marine 5200, but how do I keep it all together to seal while the silicone dries without taking the entire top off?  Best I can think of is to cut some plywood to be bigger than the window, then lower the top enough to rest on the plywood and then weight down the edges.  
 

Any ideas or experience with this? 

Glue it with the best stuff you can find and support it somehow with a physical item keep them in close contact.

Once it's glued, I'd also go around and follow up with masking or some other tape to keep it more firmly in contact directly over where it's glued.

I have the same issue with the wife's A4... watching this with interest.

People that have done this job on u-tube are using suction cup clamps.

Edit:  Like so:  https://www.amazon.com/Giant-Suction-Clamps-Convertible-Windshield/dp/B07412HKZV

You are not alone.

This happened to DD#1's Miat.  We tried unsuccessfully to fix it with Gorilla Glue and some big magnets to clamp it.  Consensus in the Miata world was that a new top was in order.

If it's a Robbins top, it seems like they have an unfortunate trend of doing this alarmingly often lately. Saw it happen to a bunch of NC Miata guys back when I was in that group.

No clue on the brand of top, was on the car when I got it.  It seems decent quality otherwise.  
 

Before I spend $1100 and a weekend on a new top, it seems worth trying to fix.   With clean mating surfaces, some window weld and a combination of the suction cup clamp things, rare earth bar magnets, and supporting wood, it might just work.  Worst case I have to buy a top, which is back where I started.   

3M Windo-Weld with single-step primer, see also:

https://grassrootsmotorsports.com/forum/grm/convertible-top-glass-window-fell-out-boxster-help/271508/page1/

Sonic said:

No clue on the brand of top, was on the car when I got it.  It seems decent quality otherwise.  
 

Before I spend $1100 and a weekend on a new top, it seems worth trying to fix.   With clean mating surfaces, some window weld and a combination of the suction cup clamp things, rare earth bar magnets, and supporting wood, it might just work.  Worst case I have to buy a top, which is back where I started.   

I've got everything you need.  Text me.

Are you a PCA member? Go to the next monthly meeting and ask if any other Boxster owners are interested in a work party. I'd bet that there are at least a couple of members who would like to learn how to do this and at least a couple more who have already done it and want to teach others. You might even find a local shop who would be interested in hosting the event some evening. A lot of PCA regions love this kind of stuff. 

Its a dang messy job.