Im not sure if it will work but, could youjust use extra silicone tubeing and attach that to the end of your muffler and bring it down under yourfuselage or something similar to that?

same here, most of the people at my field who have deadsticks....run those...once we take them off.....no problems. some engines run just fine with a small rpm loss, most dont.
despite the fast supertiger engines have a boat anchor of a muffler they are easy to adjust so you dont get slime all over your plane

 Those exhaust deflectors need to be fitted properly or else the airstream tends to bend them back and they restrict the exhaust outlet. Thats when the power is robbed.
That said, I rarely use on e because any increase in length of the outlet is a restriction and that can be measured in meaning rpm loss.
Its less of an issue with more powerful engine but with the little .061 and smaller its noticable

I used them from day one on most of the two strokes i have owned. As for robbing power?? Nothing I have ever noticed but I'm sure they do to a small degree. My trick for keeping them on is to run a bead of JB Weld around the muffler tip so the extension has a lip to be tightened around. I only have one two stroke engine being used at the moment and it has the deflector on it. Due to engine location it doesn't help deflect the snot very much. This is a bigger engine though, an SK .90 but I even use them on the OS .40 LA when I run the engine on a trainer.