maybe you could post a picture.
perhaps try bringing the cover back up to heat and try scraping while it's hot.
next would be going to the hardware store and getting some emery cloth. some persistence with about #1000 would bring you through the aluminum foil layer. of course, be careful not to overdo it and go through the enamel layer. the area you've rubbed would be matt, but a little further use of some elbow grease and #1500, #2000, #3000 & perhaps #4000 emery cloth would bring it to a respectable gloss surface. if there are actually blobs of molten aluminum, things such as jewelers files, coarse sharpening stone, or grinder would get through the bulk of it more or less quickly.
someone at a hardware store may know of some kind of caustic that would corrode aluminum, but leave the enamel surface ok.
another thing you might try ,though extreme, would be this. aluminum foil is thin enough to actually vaporize when a high enough heat, such as a propane torch, is applied. if the cover has some small sections that are hidden from sight when in place, you could first try slowly heating up that section with a blow torch to see if it would damage the cover or not. of course, stop as soon as any damage to the enamel or whatever seems about to happen. if it seems to take the high heat well, you could then apply the flame directly to the aluminum foil.
best of luck.