People can't read thoughts and can't really know what are things that could comfort you through grief. Usually people either copy what is the social norm where you live by in expressing condolences, or they try to say things they would imagine be supportive in your situation.
If this is in your location a common way to express support and condolence, you will have a tough time in spreading the news that you don't want it to be expressed that way. Moreover correcting people is going to be a bit confrontational as it is ending in a request for them to stop something, and can be seen a bit like a demand in the NVC sense.
It is possible to request that though. Since you want to be gentle (I understand, avoid conflict), I believe NVC is a fine tool, and it would advise there to express your request positively (request to do something instead of stopping something). This is an example using a bit of deception, but firm enough to hint someone a praise wording isn't appropriate:
This is a difficult/painful subject and I would prefer we speak about something else.
You could be also more precise according to how much you are comfortable with that:
I don't like one assumes my mom's intention. Could you praise me directly next time ?
I would expect most people to understand and respect your request even if it could be that some people don't understand why expression of their good feelings got rejected. Since I'm not sure explaining your reasons would help very much, you could instead close the subject with a reassuring statement that you appreciate the intention to support you they had.