While I've never actually taken the actual bit of glass out of a sunroof frame before (typically, new sunroofs come in frames, so it's just a bolt job) I see no reason why you can't remove it, provided there's access to the bond to cut through.

Pics aren't really clear, but if there is room to get to the bond all the way round, from the inside, then I'd do it using one of these;



But with non-segmented blades (as they are crap and keep breaking apart when you put too much pressure on them).

Protect the glass best you can, both inside and out, as it will be easy to scratch it. I'd advise sticky back plastic (the thicker the better) on the outside, and lay it flat on a bench on a towel. That way, the plastic protects from scratches, the towel acts as a soft surface, and should the worst happen and you blow the glass up, the plastic will keep it all together, bit like window tints. On the inside I'd plastic it again, then get some card or something to go between it and your hand / knife handle.

Get a squirty bottle (with jet spray, rather than fan spray) and fill it will screen wash. Use this to squirt along the bond line where you're cutting; acts as a lubricant. Don't use silicone spray or grease, as it's a nightmare to fully clean off, and if it's not all gone, it'll make rebonding it a nightmare. Spray 4-6" at a time, and use long, sweeping strokes with the blade - don't try to cut through the bond completely each time. The name of the game is let the blade do the work, not your arm. Bit like drilling; less pressure, and let the bit do the drilling. Don't be afraid to go through a WHOLE pack of blades either. Nothing worse than trying to cut out glass with a blunt blade.

Neil mentioned the wire - this will work, but only if there is clear access between the glass on both the outside AND inside. You fit the wire all the way round the outside, feed it through the bond and inside the frame, and you cut inwards. Not gonna be easy to do on your own with it out the car on a bench, and very easy to get the angles wrong, snap the wire, and either punch yourself in the chest, or knuckle-bump the inner frame, loosing your knuckles! If you don't have clear access to the bond line, forget it. You'll just chew through whatever seal there is around it, and probably catch the wire on a lug or bolt inside and it'll snap.

I'd really need to see it in person, but I'd say the knife is probably the best bet