I have managed to modify the ievo firmware (2.3) so that it will let user switch to DSi mode from a DSL. It might be really useful for 3DS or new firware DSi that can't run the DSL mode any more to make this task.
Notes

* use the nds file only to switch ievo into DSi mode and nothing else !
* when dsi mode is enable, you won't be able to use your ievo on DSL anymore, unless you switch back
* it has been tested only on a DSL and ievo bootstrap 1.1 EUR. There is high probabilty it works on US region also, but not tested.
* the region test (ievo region == dsi/3ds region) has been disable, so check your ievo region !
* use it at your own risk... (but it worked perfectly on my ievo...)

Instructions

boot your ievo on dsl
launch the nds file as an homebrew (see link below)
As the file is a firmware, an exact display from ievo menu will appear
go to settings and select "boot from slot-2" (I was too lazy to change this value)
a message will show up saying that you are in DSi mode
switch off your DSL, and insert your ievo on a DSi/3DS, and that's it !

3DS users Note: iEVO starts out in DSL mode, so if you don't have a DSi, then you can't switch your iEVO into DSi mode. For the DSi, the latest DSi FW update (1.4.3) breaks DSL mode, which means you can't even boot your iEVO on your DSi in order to switch it to DSi mode.

Download: CycloDS iEvolution DSi-Mode Swit... 9/27/11 download on FileTrip.net - FileTrip
Source: Switch ievo mode to DSi from a DSL - GBAtemp.net