This would work, but I'd worry about capping a bottle of actively fermenting beer, even though it's going in the fridge. I think a better approach would be: after racking off the yeast/dregs from the primary, just pour some slurry into a sanitized jar. I like honey jars for this, because they have a wide mouth. Put some saran wrap over the top & screw on the lid. This is not airtight enough to explode the jar, but it's sealed well enough for your purposes. Go ahead and keep it for 4 weeks - it will wake up just fine. Doing an acid yeast wash is the preferred method, but if you just want to get one more batch from it, and your primary was infection free, this will work.