there is not one. and there may not be a good way to make one.
the way priiloader's "forwarder" as you call it works is setting a flag that you want to access the priiloader menu. then it boots priiloader, and priiloader sees this flag and says' "ok, here's the menu". since 0.29 is not looking for that flag which the priiloader "forwarder" sets, you will need to use another method to tell preloader to show you the menu. since 0.29 was not open source, only crediar knows for sure, but i assume that there are only 2 flags that will cause preloader 0.29 to show its menu 100% of the time.
1 - hold down the reset button
2 - have the "return to" setting return to preloader.
now it is very easy to write the settings to tell preloader to show its menu and then load preloader so it reads those settings and shows the menu. but the trouble comes in the fact that this is not temporary. if you write the settings to show the preloader menu, then there is nothing that is writing the settings back to NOT return to preloader when you don't want to. and since you are wanting this channel in the first place, it means that you don't want preloader to always show itself.
so it seems that if somebody did use this method to make the 0.29 forwarder, it would only work 1 time. then you would have to manually change the settings in preloader. and each time you used the channel, you would have to redo your settings.
you better just sit at your sofa and use a broomstick to hold reset.