Without pictures I probably could only make some suggestions.
Have you tried using a bolt extractor? There are a couple depending on the situation. The links I am providing are just for reference.
1.) Socket set (
link)
2.) Drill Set (
link), but requires a bit of room.
3.) Weld another bolt on and pull on that. (If you have access to a welder).
4.) Fill with polyurethane (
link). You may be able to do this without even taking the mount out of the car and the one I am suggesting can usually be bought at most hardware stores. Just be sure you have enough drying time (usually 24 hours) and the bolt is approximately the center of the mount (lift engine with jack or lower subframe for alignment).
5.) J.B. Weld could be used to make up for the rounded edges of the bolt, or even to weld a sacrificial socket to the bolt. Just make sure you don't weld the parts to the mount/engine. I'd probably use the fast weld stuff since you aren't worried about heat in this case. I usually use masking tape and/or vaseline to keep it from getting where I don't want it. Keep in mind that JB Weld will be runny during the cure time.
6.) Go crazy and bolt/weld a chain to the mount and the subframe or somewhere further back. Just leave enough slack to allow for some movement, but I would suggest no more than 1.0".
I'll assume you are referring to the front mount being that you are talking about forward issues. You can lower the subframe about 2-3 inches, which may be more than enough. You just need to be able to support the mid part of the car, and the subframe separately. I have a floor jack attachment which allows me to reach both sides of the subframe at the same time which makes doing something like this fairly simple. You will have 4 x 18mm bolts to remove and lower the subframe. Just don't let it go too low, otherwise you could damage things like steering, break lines etc. 3" would be stretching it in most cases, but you can just loosen the rear bolts just enough to allow the front to lower more if you let them hang.
Alternatively you can usually get enough space from the top side if you remove the cooling fans. This might work good if you wanted to just fill the bushing. At least you know now it's not something serious, but should be addressed soon as if you have all the bushing gone it can quickly wear out the others.
Have even see damage depending on other things failing. These cars don't have dog bones to account for issues like this.
Hope this helps.
